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Cleaned up formatting and clarified output
Unified the formatting throughout the document, clarified the output of a few lines, and tried to make it easier to visually separate comments from code when reading.
This commit is contained in:
Dillon J Byrne
parent
96bb814889
commit
518a383de1
@ -33,27 +33,27 @@ Note: This article applies to Python 3 specifically. Check out [here](http://lea
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3 # => 3
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# Math is what you would expect
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1 + 1 # => 2
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8 - 1 # => 7
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1 + 1 # => 2
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8 - 1 # => 7
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10 * 2 # => 20
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# Except division which returns floats, real numbers, by default
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35 / 5 # => 7.0
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# Result of integer division truncated down both for positive and negative.
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5 // 3 # => 1
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5.0 // 3.0 # => 1.0 # works on floats too
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-5 // 3 # => -2
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-5.0 // 3.0 # => -2.0
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5 // 3 # => 1
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5.0 // 3.0 # => 1.0 # works on floats too
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-5 // 3 # => -2
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-5.0 // 3.0 # => -2.0
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# When you use a float, results are floats
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3 * 2.0 # => 6.0
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3 * 2.0 # => 6.0
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# Modulo operation
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7 % 3 # => 1
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7 % 3 # => 1
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# Exponentiation (x**y, x to the yth power)
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2**4 # => 16
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2**4 # => 16
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# Enforce precedence with parentheses
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(1 + 3) * 2 # => 8
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@ -63,20 +63,20 @@ True
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False
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# negate with not
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not True # => False
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not True # => False
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not False # => True
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# Boolean Operators
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# Note "and" and "or" are case-sensitive
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True and False #=> False
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False or True #=> True
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True and False # => False
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False or True # => True
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# Note using Bool operators with ints
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0 and 2 #=> 0
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-5 or 0 #=> -5
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0 == False #=> True
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2 == True #=> False
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1 == True #=> True
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0 and 2 # => 0
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-5 or 0 # => -5
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0 == False # => True
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2 == True # => False
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1 == True # => True
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# Equality is ==
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1 == 1 # => True
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@ -98,13 +98,13 @@ False or True #=> True
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# (is vs. ==) is checks if two variable refer to the same object, but == checks
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# if the objects pointed to have the same values.
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a = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
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b = a # Point b at what a is pointing to
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b is a # => True, a and b refer to the same object
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b == a # => True, a's and b's objects are equal
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b = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
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b is a # => False, a and b do not refer to the same object
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b == a # => True, a's and b's objects are equal
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a = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
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b = a # Point b at what a is pointing to
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b is a # => True, a and b refer to the same object
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b == a # => True, a's and b's objects are equal
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b = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4]
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b is a # => False, a and b do not refer to the same object
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b == a # => True, a's and b's objects are equal
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# Strings are created with " or '
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"This is a string."
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@ -113,24 +113,24 @@ b == a # => True, a's and b's objects are equal
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# Strings can be added too! But try not to do this.
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"Hello " + "world!" # => "Hello world!"
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# Strings can be added without using '+'
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"Hello " "world!" # => "Hello world!"
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"Hello " "world!" # => "Hello world!"
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# A string can be treated like a list of characters
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"This is a string"[0] # => 'T'
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# .format can be used to format strings, like this:
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"{} can be {}".format("strings", "interpolated")
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"{} can be {}".format("Strings", "interpolated") # => "Strings can be interpolated"
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# You can repeat the formatting arguments to save some typing.
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"{0} be nimble, {0} be quick, {0} jump over the {1}".format("Jack", "candle stick")
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#=> "Jack be nimble, Jack be quick, Jack jump over the candle stick"
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# => "Jack be nimble, Jack be quick, Jack jump over the candle stick"
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# You can use keywords if you don't want to count.
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"{name} wants to eat {food}".format(name="Bob", food="lasagna") #=> "Bob wants to eat lasagna"
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"{name} wants to eat {food}".format(name="Bob", food="lasagna") # => "Bob wants to eat lasagna"
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# If your Python 3 code also needs to run on Python 2.5 and below, you can also
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# still use the old style of formatting:
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"%s can be %s the %s way" % ("strings", "interpolated", "old")
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"%s can be %s the %s way" % ("Strings", "interpolated", "old") # => "Strings can be interpolated the old way"
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# None is an object
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@ -139,14 +139,14 @@ None # => None
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# Don't use the equality "==" symbol to compare objects to None
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# Use "is" instead. This checks for equality of object identity.
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"etc" is None # => False
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None is None # => True
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None is None # => True
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# None, 0, and empty strings/lists/dicts all evaluate to False.
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# All other values are True
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bool(0) # => False
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bool(0) # => False
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bool("") # => False
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bool([]) #=> False
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bool({}) #=> False
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bool([]) # => False
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bool({}) # => False
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####################################################
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@ -154,11 +154,11 @@ bool({}) #=> False
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####################################################
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# Python has a print function
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print("I'm Python. Nice to meet you!")
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print("I'm Python. Nice to meet you!") # => I'm Python. Nice to meet you!
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# By default the print function also prints out a newline at the end.
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# Use the optional argument end to change the end character.
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print("Hello, World", end="!") # => Hello, World!
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print("Hello, World", end="!") # => Hello, World!
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# No need to declare variables before assigning to them.
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# Convention is to use lower_case_with_underscores
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@ -185,7 +185,7 @@ li.pop() # => 3 and li is now [1, 2, 4]
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li.append(3) # li is now [1, 2, 4, 3] again.
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# Access a list like you would any array
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li[0] # => 1
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li[0] # => 1
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# Look at the last element
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li[-1] # => 3
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@ -194,61 +194,61 @@ li[4] # Raises an IndexError
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# You can look at ranges with slice syntax.
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# (It's a closed/open range for you mathy types.)
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li[1:3] # => [2, 4]
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li[1:3] # => [2, 4]
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# Omit the beginning
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li[2:] # => [4, 3]
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li[2:] # => [4, 3]
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# Omit the end
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li[:3] # => [1, 2, 4]
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li[:3] # => [1, 2, 4]
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# Select every second entry
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li[::2] # =>[1, 4]
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# Return a reversed copy of the list
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li[::-1] # => [3, 4, 2, 1]
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li[::-1] # => [3, 4, 2, 1]
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# Use any combination of these to make advanced slices
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# li[start:end:step]
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# Make a one layer deep copy using slices
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li2 = li[:] # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false.
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li2 = li[:] # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false.
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# Remove arbitrary elements from a list with "del"
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del li[2] # li is now [1, 2, 3]
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del li[2] # li is now [1, 2, 3]
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# You can add lists
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# Note: values for li and for other_li are not modified.
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li + other_li # => [1, 2, 3, 4, 5, 6]
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li + other_li # => [1, 2, 3, 4, 5, 6]
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# Concatenate lists with "extend()"
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li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
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li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
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# Check for existence in a list with "in"
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1 in li # => True
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1 in li # => True
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# Examine the length with "len()"
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len(li) # => 6
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len(li) # => 6
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# Tuples are like lists but are immutable.
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tup = (1, 2, 3)
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tup[0] # => 1
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tup[0] # => 1
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tup[0] = 3 # Raises a TypeError
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# Note that a tuple of length one has to have a comma after the last element but
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# tuples of other lengths, even zero, do not.
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type((1)) # => <class 'int'>
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type((1,)) # => <class 'tuple'>
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type(()) # => <class 'tuple'>
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type((1)) # => <class 'int'>
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type((1,)) # => <class 'tuple'>
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type(()) # => <class 'tuple'>
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# You can do most of the list operations on tuples too
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len(tup) # => 3
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tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
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tup[:2] # => (1, 2)
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2 in tup # => True
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len(tup) # => 3
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tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
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tup[:2] # => (1, 2)
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2 in tup # => True
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# You can unpack tuples (or lists) into variables
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a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
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a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
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# Tuples are created by default if you leave out the parentheses
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d, e, f = 4, 5, 6
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# Now look how easy it is to swap two values
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e, d = d, e # d is now 5 and e is now 4
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e, d = d, e # d is now 5 and e is now 4
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# Dictionaries store mappings
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@ -259,45 +259,45 @@ filled_dict = {"one": 1, "two": 2, "three": 3}
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# Note keys for dictionaries have to be immutable types. This is to ensure that
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# the key can be converted to a constant hash value for quick look-ups.
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# Immutable types include ints, floats, strings, tuples.
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invalid_dict = {[1,2,3]: "123"} # => Raises a TypeError: unhashable type: 'list'
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valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however.
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invalid_dict = {[1,2,3]: "123"} # => Raises a TypeError: unhashable type: 'list'
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valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however.
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# Look up values with []
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filled_dict["one"] # => 1
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filled_dict["one"] # => 1
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# Get all keys as an iterable with "keys()". We need to wrap the call in list()
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# to turn it into a list. We'll talk about those later. Note - Dictionary key
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# ordering is not guaranteed. Your results might not match this exactly.
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list(filled_dict.keys()) # => ["three", "two", "one"]
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list(filled_dict.keys()) # => ["three", "two", "one"]
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# Get all values as an iterable with "values()". Once again we need to wrap it
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# in list() to get it out of the iterable. Note - Same as above regarding key
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# ordering.
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list(filled_dict.values()) # => [3, 2, 1]
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list(filled_dict.values()) # => [3, 2, 1]
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# Check for existence of keys in a dictionary with "in"
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"one" in filled_dict # => True
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1 in filled_dict # => False
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"one" in filled_dict # => True
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1 in filled_dict # => False
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# Looking up a non-existing key is a KeyError
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filled_dict["four"] # KeyError
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filled_dict["four"] # KeyError
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# Use "get()" method to avoid the KeyError
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filled_dict.get("one") # => 1
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filled_dict.get("four") # => None
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filled_dict.get("one") # => 1
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filled_dict.get("four") # => None
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# The get method supports a default argument when the value is missing
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filled_dict.get("one", 4) # => 1
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filled_dict.get("four", 4) # => 4
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filled_dict.get("four", 4) # => 4
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# "setdefault()" inserts into a dictionary only if the given key isn't present
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filled_dict.setdefault("five", 5) # filled_dict["five"] is set to 5
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filled_dict.setdefault("five", 6) # filled_dict["five"] is still 5
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# Adding to a dictionary
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filled_dict.update({"four":4}) #=> {"one": 1, "two": 2, "three": 3, "four": 4}
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#filled_dict["four"] = 4 #another way to add to dict
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filled_dict.update({"four":4}) # => {"one": 1, "two": 2, "three": 3, "four": 4}
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#filled_dict["four"] = 4 #another way to add to dict
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# Remove keys from a dictionary with del
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del filled_dict["one"] # Removes the key "one" from filled dict
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@ -306,31 +306,31 @@ del filled_dict["one"] # Removes the key "one" from filled dict
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# Sets store ... well sets
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empty_set = set()
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# Initialize a set with a bunch of values. Yeah, it looks a bit like a dict. Sorry.
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some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4}
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some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4}
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# Similar to keys of a dictionary, elements of a set have to be immutable.
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invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list'
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invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list'
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valid_set = {(1,), 1}
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# Can set new variables to a set
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filled_set = some_set
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# Add one more item to the set
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filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
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filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
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# Do set intersection with &
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other_set = {3, 4, 5, 6}
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filled_set & other_set # => {3, 4, 5}
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filled_set & other_set # => {3, 4, 5}
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# Do set union with |
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filled_set | other_set # => {1, 2, 3, 4, 5, 6}
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filled_set | other_set # => {1, 2, 3, 4, 5, 6}
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# Do set difference with -
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{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
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{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
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# Check for existence in a set with in
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2 in filled_set # => True
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10 in filled_set # => False
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10 in filled_set # => False
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@ -416,12 +416,12 @@ try:
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# Use "raise" to raise an error
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raise IndexError("This is an index error")
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except IndexError as e:
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pass # Pass is just a no-op. Usually you would do recovery here.
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pass # Pass is just a no-op. Usually you would do recovery here.
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except (TypeError, NameError):
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pass # Multiple exceptions can be handled together, if required.
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else: # Optional clause to the try/except block. Must follow all except blocks
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pass # Multiple exceptions can be handled together, if required.
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else: # Optional clause to the try/except block. Must follow all except blocks
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print("All good!") # Runs only if the code in try raises no exceptions
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finally: # Execute under all circumstances
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finally: # Execute under all circumstances
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print("We can clean up resources here")
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# Instead of try/finally to cleanup resources you can use a with statement
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@ -435,11 +435,11 @@ with open("myfile.txt") as f:
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filled_dict = {"one": 1, "two": 2, "three": 3}
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our_iterable = filled_dict.keys()
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print(our_iterable) #=> range(1,10). This is an object that implements our Iterable interface
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print(our_iterable) # => range(1,10). This is an object that implements our Iterable interface
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# We can loop over it.
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for i in our_iterable:
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print(i) # Prints one, two, three
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print(i) # Prints one, two, three
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# However we cannot address elements by index.
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our_iterable[1] # Raises a TypeError
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@ -449,17 +449,17 @@ our_iterator = iter(our_iterable)
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# Our iterator is an object that can remember the state as we traverse through it.
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# We get the next object with "next()".
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next(our_iterator) #=> "one"
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next(our_iterator) # => "one"
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# It maintains state as we iterate.
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next(our_iterator) #=> "two"
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next(our_iterator) #=> "three"
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next(our_iterator) # => "two"
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next(our_iterator) # => "three"
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# After the iterator has returned all of its data, it gives you a StopIterator Exception
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next(our_iterator) # Raises StopIteration
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next(our_iterator) # Raises StopIteration
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# You can grab all the elements of an iterator by calling list() on it.
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list(filled_dict.keys()) #=> Returns ["one", "two", "three"]
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list(filled_dict.keys()) # => Returns ["one", "two", "three"]
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####################################################
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@ -469,20 +469,20 @@ list(filled_dict.keys()) #=> Returns ["one", "two", "three"]
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# Use "def" to create new functions
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def add(x, y):
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print("x is {} and y is {}".format(x, y))
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return x + y # Return values with a return statement
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return x + y # Return values with a return statement
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# Calling functions with parameters
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add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
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add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
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# Another way to call functions is with keyword arguments
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add(y=6, x=5) # Keyword arguments can arrive in any order.
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add(y=6, x=5) # Keyword arguments can arrive in any order.
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# You can define functions that take a variable number of
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# positional arguments
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def varargs(*args):
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return args
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varargs(1, 2, 3) # => (1, 2, 3)
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varargs(1, 2, 3) # => (1, 2, 3)
|
||||
|
||||
# You can define functions that take a variable number of
|
||||
# keyword arguments, as well
|
||||
@ -490,7 +490,7 @@ def keyword_args(**kwargs):
|
||||
return kwargs
|
||||
|
||||
# Let's call it to see what happens
|
||||
keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
|
||||
keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
|
||||
|
||||
|
||||
# You can do both at once, if you like
|
||||
@ -507,33 +507,33 @@ all_the_args(1, 2, a=3, b=4) prints:
|
||||
# Use * to expand tuples and use ** to expand kwargs.
|
||||
args = (1, 2, 3, 4)
|
||||
kwargs = {"a": 3, "b": 4}
|
||||
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
|
||||
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
|
||||
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
|
||||
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
|
||||
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
|
||||
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
|
||||
|
||||
# Returning multiple values (with tuple assignments)
|
||||
def swap(x, y):
|
||||
return y, x # Return multiple values as a tuple without the parenthesis.
|
||||
# (Note: parenthesis have been excluded but can be included)
|
||||
return y, x # Return multiple values as a tuple without the parenthesis.
|
||||
# (Note: parenthesis have been excluded but can be included)
|
||||
|
||||
x = 1
|
||||
y = 2
|
||||
x, y = swap(x, y) # => x = 2, y = 1
|
||||
# (x, y) = swap(x,y) # Again parenthesis have been excluded but can be included.
|
||||
x, y = swap(x, y) # => x = 2, y = 1
|
||||
# (x, y) = swap(x,y) # Again parenthesis have been excluded but can be included.
|
||||
|
||||
# Function Scope
|
||||
x = 5
|
||||
|
||||
def setX(num):
|
||||
# Local var x not the same as global variable x
|
||||
x = num # => 43
|
||||
print (x) # => 43
|
||||
x = num # => 43
|
||||
print (x) # => 43
|
||||
|
||||
def setGlobalX(num):
|
||||
global x
|
||||
print (x) # => 5
|
||||
x = num # global var x is now set to 6
|
||||
print (x) # => 6
|
||||
print (x) # => 5
|
||||
x = num # global var x is now set to 6
|
||||
print (x) # => 6
|
||||
|
||||
setX(43)
|
||||
setGlobalX(6)
|
||||
@ -549,20 +549,20 @@ add_10 = create_adder(10)
|
||||
add_10(3) # => 13
|
||||
|
||||
# There are also anonymous functions
|
||||
(lambda x: x > 2)(3) # => True
|
||||
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
|
||||
(lambda x: x > 2)(3) # => True
|
||||
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
|
||||
|
||||
# TODO - Fix for iterables
|
||||
# There are built-in higher order functions
|
||||
map(add_10, [1, 2, 3]) # => [11, 12, 13]
|
||||
map(max, [1, 2, 3], [4, 2, 1]) # => [4, 2, 3]
|
||||
map(add_10, [1, 2, 3]) # => [11, 12, 13]
|
||||
map(max, [1, 2, 3], [4, 2, 1]) # => [4, 2, 3]
|
||||
|
||||
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
|
||||
# We can use list comprehensions for nice maps and filters
|
||||
# List comprehension stores the output as a list which can itself be a nested list
|
||||
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
|
||||
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
|
||||
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
|
||||
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
|
||||
|
||||
####################################################
|
||||
## 5. Classes
|
||||
@ -609,15 +609,15 @@ j = Human("Joel")
|
||||
print(j.say("hello")) # prints out "Joel: hello"
|
||||
|
||||
# Call our class method
|
||||
i.get_species() # => "H. sapiens"
|
||||
i.get_species() # => "H. sapiens"
|
||||
|
||||
# Change the shared attribute
|
||||
Human.species = "H. neanderthalensis"
|
||||
i.get_species() # => "H. neanderthalensis"
|
||||
j.get_species() # => "H. neanderthalensis"
|
||||
i.get_species() # => "H. neanderthalensis"
|
||||
j.get_species() # => "H. neanderthalensis"
|
||||
|
||||
# Call the static method
|
||||
Human.grunt() # => "*grunt*"
|
||||
Human.grunt() # => "*grunt*"
|
||||
|
||||
|
||||
####################################################
|
||||
@ -630,8 +630,8 @@ print(math.sqrt(16)) # => 4
|
||||
|
||||
# You can get specific functions from a module
|
||||
from math import ceil, floor
|
||||
print(ceil(3.7)) # => 4.0
|
||||
print(floor(3.7)) # => 3.0
|
||||
print(ceil(3.7)) # => 4.0
|
||||
print(floor(3.7)) # => 3.0
|
||||
|
||||
# You can import all functions from a module.
|
||||
# Warning: this is not recommended
|
||||
@ -639,7 +639,7 @@ from math import *
|
||||
|
||||
# You can shorten module names
|
||||
import math as m
|
||||
math.sqrt(16) == m.sqrt(16) # => True
|
||||
math.sqrt(16) == m.sqrt(16) # => True
|
||||
|
||||
# Python modules are just ordinary python files. You
|
||||
# can write your own, and import them. The name of the
|
||||
@ -698,7 +698,7 @@ def say(say_please=False):
|
||||
return msg, say_please
|
||||
|
||||
|
||||
print(say()) # Can you buy me a beer?
|
||||
print(say()) # Can you buy me a beer?
|
||||
print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :(
|
||||
```
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user