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Diffstat (limited to 'python3.html.markdown')
| -rw-r--r-- | python3.html.markdown | 524 |
1 files changed, 354 insertions, 170 deletions
diff --git a/python3.html.markdown b/python3.html.markdown index 87fa0b70..6b3486a6 100644 --- a/python3.html.markdown +++ b/python3.html.markdown @@ -5,6 +5,7 @@ contributors: - ["Steven Basart", "http://github.com/xksteven"] - ["Andre Polykanine", "https://github.com/Oire"] - ["Zachary Ferguson", "http://github.com/zfergus2"] + - ["evuez", "http://github.com/evuez"] filename: learnpython3.py --- @@ -33,27 +34,27 @@ Note: This article applies to Python 3 specifically. Check out [here](http://lea 3 # => 3 # Math is what you would expect -1 + 1 # => 2 -8 - 1 # => 7 +1 + 1 # => 2 +8 - 1 # => 7 10 * 2 # => 20 # Except division which returns floats, real numbers, by default 35 / 5 # => 7.0 # Result of integer division truncated down both for positive and negative. -5 // 3 # => 1 -5.0 // 3.0 # => 1.0 # works on floats too --5 // 3 # => -2 --5.0 // 3.0 # => -2.0 +5 // 3 # => 1 +5.0 // 3.0 # => 1.0 # works on floats too +-5 // 3 # => -2 +-5.0 // 3.0 # => -2.0 # When you use a float, results are floats -3 * 2.0 # => 6.0 +3 * 2.0 # => 6.0 # Modulo operation -7 % 3 # => 1 +7 % 3 # => 1 # Exponentiation (x**y, x to the yth power) -2**4 # => 16 +2**4 # => 16 # Enforce precedence with parentheses (1 + 3) * 2 # => 8 @@ -63,20 +64,20 @@ True False # negate with not -not True # => False +not True # => False not False # => True # Boolean Operators # Note "and" and "or" are case-sensitive -True and False #=> False -False or True #=> True +True and False # => False +False or True # => True # Note using Bool operators with ints -0 and 2 #=> 0 --5 or 0 #=> -5 -0 == False #=> True -2 == True #=> False -1 == True #=> True +0 and 2 # => 0 +-5 or 0 # => -5 +0 == False # => True +2 == True # => False +1 == True # => True # Equality is == 1 == 1 # => True @@ -96,15 +97,15 @@ False or True #=> True 1 < 2 < 3 # => True 2 < 3 < 2 # => False -# (is vs. ==) is checks if two variable refer to the same object, but == checks +# (is vs. ==) is checks if two variables refer to the same object, but == checks # if the objects pointed to have the same values. -a = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4] -b = a # Point b at what a is pointing to -b is a # => True, a and b refer to the same object -b == a # => True, a's and b's objects are equal -b = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4] -b is a # => False, a and b do not refer to the same object -b == a # => True, a's and b's objects are equal +a = [1, 2, 3, 4] # Point a at a new list, [1, 2, 3, 4] +b = a # Point b at what a is pointing to +b is a # => True, a and b refer to the same object +b == a # => True, a's and b's objects are equal +b = [1, 2, 3, 4] # Point b at a new list, [1, 2, 3, 4] +b is a # => False, a and b do not refer to the same object +b == a # => True, a's and b's objects are equal # Strings are created with " or ' "This is a string." @@ -113,24 +114,27 @@ b == a # => True, a's and b's objects are equal # Strings can be added too! But try not to do this. "Hello " + "world!" # => "Hello world!" # Strings can be added without using '+' -"Hello " "world!" # => "Hello world!" +"Hello " "world!" # => "Hello world!" # A string can be treated like a list of characters "This is a string"[0] # => 'T' +# You can find the length of a string +len("This is a string") # => 16 + # .format can be used to format strings, like this: -"{} can be {}".format("strings", "interpolated") +"{} can be {}".format("Strings", "interpolated") # => "Strings can be interpolated" # You can repeat the formatting arguments to save some typing. "{0} be nimble, {0} be quick, {0} jump over the {1}".format("Jack", "candle stick") -#=> "Jack be nimble, Jack be quick, Jack jump over the candle stick" +# => "Jack be nimble, Jack be quick, Jack jump over the candle stick" # You can use keywords if you don't want to count. -"{name} wants to eat {food}".format(name="Bob", food="lasagna") #=> "Bob wants to eat lasagna" +"{name} wants to eat {food}".format(name="Bob", food="lasagna") # => "Bob wants to eat lasagna" # If your Python 3 code also needs to run on Python 2.5 and below, you can also # still use the old style of formatting: -"%s can be %s the %s way" % ("strings", "interpolated", "old") +"%s can be %s the %s way" % ("Strings", "interpolated", "old") # => "Strings can be interpolated the old way" # None is an object @@ -139,14 +143,14 @@ None # => None # Don't use the equality "==" symbol to compare objects to None # Use "is" instead. This checks for equality of object identity. "etc" is None # => False -None is None # => True +None is None # => True # None, 0, and empty strings/lists/dicts all evaluate to False. # All other values are True -bool(0) # => False +bool(0) # => False bool("") # => False -bool([]) #=> False -bool({}) #=> False +bool([]) # => False +bool({}) # => False #################################################### @@ -154,11 +158,15 @@ bool({}) #=> False #################################################### # Python has a print function -print("I'm Python. Nice to meet you!") +print("I'm Python. Nice to meet you!") # => I'm Python. Nice to meet you! # By default the print function also prints out a newline at the end. # Use the optional argument end to change the end character. -print("Hello, World", end="!") # => Hello, World! +print("Hello, World", end="!") # => Hello, World! + +# Simple way to get input data from console +input_string_var = input("Enter some data: ") # Returns the data as a string +# Note: In earlier versions of Python, input() method was named as raw_input() # No need to declare variables before assigning to them. # Convention is to use lower_case_with_underscores @@ -169,6 +177,10 @@ some_var # => 5 # See Control Flow to learn more about exception handling. some_unknown_var # Raises a NameError +# if can be used as an expression +# Equivalent of C's '?:' ternary operator +"yahoo!" if 3 > 2 else 2 # => "yahoo!" + # Lists store sequences li = [] # You can start with a prefilled list @@ -185,7 +197,7 @@ li.pop() # => 3 and li is now [1, 2, 4] li.append(3) # li is now [1, 2, 4, 3] again. # Access a list like you would any array -li[0] # => 1 +li[0] # => 1 # Look at the last element li[-1] # => 3 @@ -194,61 +206,74 @@ li[4] # Raises an IndexError # You can look at ranges with slice syntax. # (It's a closed/open range for you mathy types.) -li[1:3] # => [2, 4] +li[1:3] # => [2, 4] # Omit the beginning -li[2:] # => [4, 3] +li[2:] # => [4, 3] # Omit the end -li[:3] # => [1, 2, 4] +li[:3] # => [1, 2, 4] # Select every second entry li[::2] # =>[1, 4] # Return a reversed copy of the list -li[::-1] # => [3, 4, 2, 1] +li[::-1] # => [3, 4, 2, 1] # Use any combination of these to make advanced slices # li[start:end:step] # Make a one layer deep copy using slices -li2 = li[:] # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false. +li2 = li[:] # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false. # Remove arbitrary elements from a list with "del" -del li[2] # li is now [1, 2, 3] +del li[2] # li is now [1, 2, 3] + +# Remove first occurrence of a value +li.remove(2) # li is now [1, 3] +li.remove(2) # Raises a ValueError as 2 is not in the list + +# Insert an element at a specific index +li.insert(1, 2) # li is now [1, 2, 3] again + +# Get the index of the first item found matching the argument +li.index(2) # => 1 +li.index(4) # Raises a ValueError as 4 is not in the list # You can add lists # Note: values for li and for other_li are not modified. -li + other_li # => [1, 2, 3, 4, 5, 6] +li + other_li # => [1, 2, 3, 4, 5, 6] # Concatenate lists with "extend()" -li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] +li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] # Check for existence in a list with "in" -1 in li # => True +1 in li # => True # Examine the length with "len()" -len(li) # => 6 +len(li) # => 6 # Tuples are like lists but are immutable. tup = (1, 2, 3) -tup[0] # => 1 +tup[0] # => 1 tup[0] = 3 # Raises a TypeError # Note that a tuple of length one has to have a comma after the last element but # tuples of other lengths, even zero, do not. -type((1)) # => <class 'int'> -type((1,)) # => <class 'tuple'> -type(()) # => <class 'tuple'> +type((1)) # => <class 'int'> +type((1,)) # => <class 'tuple'> +type(()) # => <class 'tuple'> # You can do most of the list operations on tuples too -len(tup) # => 3 -tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6) -tup[:2] # => (1, 2) -2 in tup # => True +len(tup) # => 3 +tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6) +tup[:2] # => (1, 2) +2 in tup # => True # You can unpack tuples (or lists) into variables -a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3 +a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3 +# You can also do extended unpacking +a, *b, c = (1, 2, 3, 4) # a is now 1, b is now [2, 3] and c is now 4 # Tuples are created by default if you leave out the parentheses d, e, f = 4, 5, 6 # Now look how easy it is to swap two values -e, d = d, e # d is now 5 and e is now 4 +e, d = d, e # d is now 5 and e is now 4 # Dictionaries store mappings @@ -259,78 +284,92 @@ filled_dict = {"one": 1, "two": 2, "three": 3} # Note keys for dictionaries have to be immutable types. This is to ensure that # the key can be converted to a constant hash value for quick look-ups. # Immutable types include ints, floats, strings, tuples. -invalid_dict = {[1,2,3]: "123"} # => Raises a TypeError: unhashable type: 'list' -valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however. +invalid_dict = {[1,2,3]: "123"} # => Raises a TypeError: unhashable type: 'list' +valid_dict = {(1,2,3):[1,2,3]} # Values can be of any type, however. # Look up values with [] -filled_dict["one"] # => 1 +filled_dict["one"] # => 1 # Get all keys as an iterable with "keys()". We need to wrap the call in list() # to turn it into a list. We'll talk about those later. Note - Dictionary key # ordering is not guaranteed. Your results might not match this exactly. -list(filled_dict.keys()) # => ["three", "two", "one"] +list(filled_dict.keys()) # => ["three", "two", "one"] # Get all values as an iterable with "values()". Once again we need to wrap it # in list() to get it out of the iterable. Note - Same as above regarding key # ordering. -list(filled_dict.values()) # => [3, 2, 1] +list(filled_dict.values()) # => [3, 2, 1] # Check for existence of keys in a dictionary with "in" -"one" in filled_dict # => True -1 in filled_dict # => False +"one" in filled_dict # => True +1 in filled_dict # => False # Looking up a non-existing key is a KeyError -filled_dict["four"] # KeyError +filled_dict["four"] # KeyError # Use "get()" method to avoid the KeyError -filled_dict.get("one") # => 1 -filled_dict.get("four") # => None +filled_dict.get("one") # => 1 +filled_dict.get("four") # => None # The get method supports a default argument when the value is missing filled_dict.get("one", 4) # => 1 -filled_dict.get("four", 4) # => 4 +filled_dict.get("four", 4) # => 4 # "setdefault()" inserts into a dictionary only if the given key isn't present filled_dict.setdefault("five", 5) # filled_dict["five"] is set to 5 filled_dict.setdefault("five", 6) # filled_dict["five"] is still 5 # Adding to a dictionary -filled_dict.update({"four":4}) #=> {"one": 1, "two": 2, "three": 3, "four": 4} -#filled_dict["four"] = 4 #another way to add to dict +filled_dict.update({"four":4}) # => {"one": 1, "two": 2, "three": 3, "four": 4} +#filled_dict["four"] = 4 #another way to add to dict # Remove keys from a dictionary with del del filled_dict["one"] # Removes the key "one" from filled dict +# From Python 3.5 you can also use the additional unpacking options +{'a': 1, **{'b': 2}} # => {'a': 1, 'b': 2} +{'a': 1, **{'a': 2}} # => {'a': 2} + + # Sets store ... well sets empty_set = set() # Initialize a set with a bunch of values. Yeah, it looks a bit like a dict. Sorry. -some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4} +some_set = {1, 1, 2, 2, 3, 4} # some_set is now {1, 2, 3, 4} # Similar to keys of a dictionary, elements of a set have to be immutable. -invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list' +invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list' valid_set = {(1,), 1} # Can set new variables to a set filled_set = some_set # Add one more item to the set -filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} +filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} # Do set intersection with & other_set = {3, 4, 5, 6} -filled_set & other_set # => {3, 4, 5} +filled_set & other_set # => {3, 4, 5} # Do set union with | -filled_set | other_set # => {1, 2, 3, 4, 5, 6} +filled_set | other_set # => {1, 2, 3, 4, 5, 6} # Do set difference with - -{1, 2, 3, 4} - {2, 3, 5} # => {1, 4} +{1, 2, 3, 4} - {2, 3, 5} # => {1, 4} + +# Do set symmetric difference with ^ +{1, 2, 3, 4} ^ {2, 3, 5} # => {1, 4, 5} + +# Check if set on the left is a superset of set on the right +{1, 2} >= {1, 2, 3} # => False + +# Check if set on the left is a subset of set on the right +{1, 2} <= {1, 2, 3} # => True # Check for existence in a set with in 2 in filled_set # => True -10 in filled_set # => False +10 in filled_set # => False @@ -393,7 +432,6 @@ by step. If step is not indicated, the default value is 1. prints: 4 6 - 8 """ for i in range(4, 8, 2): print(i) @@ -416,12 +454,12 @@ try: # Use "raise" to raise an error raise IndexError("This is an index error") except IndexError as e: - pass # Pass is just a no-op. Usually you would do recovery here. + pass # Pass is just a no-op. Usually you would do recovery here. except (TypeError, NameError): - pass # Multiple exceptions can be handled together, if required. -else: # Optional clause to the try/except block. Must follow all except blocks + pass # Multiple exceptions can be handled together, if required. +else: # Optional clause to the try/except block. Must follow all except blocks print("All good!") # Runs only if the code in try raises no exceptions -finally: # Execute under all circumstances +finally: # Execute under all circumstances print("We can clean up resources here") # Instead of try/finally to cleanup resources you can use a with statement @@ -435,11 +473,11 @@ with open("myfile.txt") as f: filled_dict = {"one": 1, "two": 2, "three": 3} our_iterable = filled_dict.keys() -print(our_iterable) #=> range(1,10). This is an object that implements our Iterable interface +print(our_iterable) # => dict_keys(['one', 'two', 'three']). This is an object that implements our Iterable interface. # We can loop over it. for i in our_iterable: - print(i) # Prints one, two, three + print(i) # Prints one, two, three # However we cannot address elements by index. our_iterable[1] # Raises a TypeError @@ -449,17 +487,17 @@ our_iterator = iter(our_iterable) # Our iterator is an object that can remember the state as we traverse through it. # We get the next object with "next()". -next(our_iterator) #=> "one" +next(our_iterator) # => "one" # It maintains state as we iterate. -next(our_iterator) #=> "two" -next(our_iterator) #=> "three" +next(our_iterator) # => "two" +next(our_iterator) # => "three" # After the iterator has returned all of its data, it gives you a StopIterator Exception -next(our_iterator) # Raises StopIteration +next(our_iterator) # Raises StopIteration # You can grab all the elements of an iterator by calling list() on it. -list(filled_dict.keys()) #=> Returns ["one", "two", "three"] +list(filled_dict.keys()) # => Returns ["one", "two", "three"] #################################################### @@ -469,20 +507,20 @@ list(filled_dict.keys()) #=> Returns ["one", "two", "three"] # Use "def" to create new functions def add(x, y): print("x is {} and y is {}".format(x, y)) - return x + y # Return values with a return statement + return x + y # Return values with a return statement # Calling functions with parameters -add(5, 6) # => prints out "x is 5 and y is 6" and returns 11 +add(5, 6) # => prints out "x is 5 and y is 6" and returns 11 # Another way to call functions is with keyword arguments -add(y=6, x=5) # Keyword arguments can arrive in any order. +add(y=6, x=5) # Keyword arguments can arrive in any order. # You can define functions that take a variable number of # positional arguments def varargs(*args): return args -varargs(1, 2, 3) # => (1, 2, 3) +varargs(1, 2, 3) # => (1, 2, 3) # You can define functions that take a variable number of # keyword arguments, as well @@ -490,7 +528,7 @@ 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 @@ -507,36 +545,36 @@ 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): +def set_x(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): +def set_global_x(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) +set_x(43) +set_global_x(6) # Python has first class functions @@ -549,25 +587,65 @@ 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] +list(map(add_10, [1, 2, 3])) # => [11, 12, 13] +list(map(max, [1, 2, 3], [4, 2, 1])) # => [4, 2, 3] -filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7] +list(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] + +# You can construct set and dict comprehensions as well. +{x for x in 'abcddeef' if x in 'abc'} # => {'d', 'e', 'f'} +{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16} + #################################################### -## 5. Classes +## 5. Modules #################################################### +# You can import modules +import math +print(math.sqrt(16)) # => 4.0 + +# 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 + +# You can import all functions from a module. +# Warning: this is not recommended +from math import * + +# You can shorten module names +import math as m +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 +# module is the same as the name of the file. + +# You can find out which functions and attributes +# defines a module. +import math +dir(math) + +# If you have a Python script named math.py in the same +# folder as your current script, the file math.py will +# be loaded instead of the built-in Python module. +# This happens because the local folder has priority +# over Python's built-in libraries. + + +#################################################### +## 6. Classes +#################################################### # We use the "class" operator to get a class class Human: @@ -585,9 +663,16 @@ class Human: # Assign the argument to the instance's name attribute self.name = name + # Initialize property + self.age = 0 + # An instance method. All methods take "self" as the first argument def say(self, msg): - return "{name}: {message}".format(name=self.name, message=msg) + print ("{name}: {message}".format(name=self.name, message=msg)) + + # Another instance method + def sing(self): + return 'yo... yo... microphone check... one two... one two...' # A class method is shared among all instances # They are called with the calling class as the first argument @@ -600,84 +685,179 @@ class Human: def grunt(): return "*grunt*" + # A property is just like a getter. + # It turns the method age() into an read-only attribute + # of the same name. + @property + def age(self): + return self._age + + # This allows the property to be set + @age.setter + def age(self, age): + self._age = age + + # This allows the property to be deleted + @age.deleter + def age(self): + del self._age + + +# When a Python interpreter reads a source file it executes all its code. +# This __name__ check makes sure this code block is only executed when this +# module is the main program. +if __name__ == '__main__': + # Instantiate a class + i = Human(name="Ian") + i.say("hi") # "Ian: hi" + j = Human("Joel") + j.say("hello") # "Joel: hello" + # i and j are instances of type Human, or in other words: they are Human objects + + # Call our class method + i.say(i.get_species()) # "Ian: H. sapiens" + # Change the shared attribute + Human.species = "H. neanderthalensis" + i.say(i.get_species()) # => "Ian: H. neanderthalensis" + j.say(j.get_species()) # => "Joel: H. neanderthalensis" + + # Call the static method + print(Human.grunt()) # => "*grunt*" + print(i.grunt()) # => "*grunt*" + + # Update the property for this instance + i.age = 42 + # Get the property + i.say(i.age) # => 42 + j.say(j.age) # => 0 + # Delete the property + del i.age + # i.age # => this would raise an AttributeError -# Instantiate a class -i = Human(name="Ian") -print(i.say("hi")) # prints out "Ian: hi" -j = Human("Joel") -print(j.say("hello")) # prints out "Joel: hello" +#################################################### +## 6.1 Multiple Inheritance +#################################################### -# Call our class method -i.get_species() # => "H. sapiens" +# Another class definition +class Bat: -# Change the shared attribute -Human.species = "H. neanderthalensis" -i.get_species() # => "H. neanderthalensis" -j.get_species() # => "H. neanderthalensis" + species = 'Baty' -# Call the static method -Human.grunt() # => "*grunt*" + def __init__(self, can_fly=True): + self.fly = can_fly + # This class also has a say method + def say(self, msg): + msg = '... ... ...' + return msg -#################################################### -## 6. Modules -#################################################### + # And its own method as well + def sonar(self): + return '))) ... (((' -# You can import modules -import math -print(math.sqrt(16)) # => 4 +if __name__ == '__main__': + b = Bat() + print(b.say('hello')) + print(b.fly) -# 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 -# You can import all functions from a module. -# Warning: this is not recommended -from math import * +# from "filename-without-extension" import "function-or-class" +from human import Human +from bat import Bat -# You can shorten module names -import math as m -math.sqrt(16) == m.sqrt(16) # => True +# Batman inherits from both Human and Bat +class Batman(Human, Bat): -# Python modules are just ordinary python files. You -# can write your own, and import them. The name of the -# module is the same as the name of the file. + # Batman has its own value for the species class attribute + species = 'Superhero' + + def __init__(self, *args, **kwargs): + # Typically to inherit attributes you have to call super: + #super(Batman, self).__init__(*args, **kwargs) + # However we are dealing with multiple inheritance here, and super() + # only works with the next base class in the MRO list. + # So instead we explicitly call __init__ for all ancestors. + # The use of *args and **kwargs allows for a clean way to pass arguments, + # with each parent "peeling a layer of the onion". + Human.__init__(self, 'anonymous', *args, **kwargs) + Bat.__init__(self, *args, can_fly=False, **kwargs) + # override the value for the name attribute + self.name = 'Sad Affleck' + + def sing(self): + return 'nan nan nan nan nan batman!' + + +if __name__ == '__main__': + sup = Batman() + + # Instance type checks + if isinstance(sup, Human): + print('I am human') + if isinstance(sup, Bat): + print('I am bat') + if type(sup) is Batman: + print('I am Batman') + + # Get the Method Resolution search Order used by both getattr() and super(). + # This attribute is dynamic and can be updated + print(Batman.__mro__) # => (<class '__main__.Batman'>, <class 'human.Human'>, <class 'bat.Bat'>, <class 'object'>) + + # Calls parent method but uses its own class attribute + print(sup.get_species()) # => Superhero + + # Calls overloaded method + print(sup.sing()) # => nan nan nan nan nan batman! + + # Calls method from Human, because inheritance order matters + sup.say('I agree') # => Sad Affleck: I agree + + # Call method that exists only in 2nd ancestor + print(sup.sonar()) # => ))) ... ((( + + # Inherited class attribute + sup.age = 100 + print(sup.age) + + # Inherited attribute from 2nd ancestor whose default value was overridden. + print('Can I fly? ' + str(sup.fly)) -# You can find out which functions and attributes -# defines a module. -import math -dir(math) #################################################### ## 7. Advanced #################################################### -# Generators help you make lazy code +# Generators help you make lazy code. def double_numbers(iterable): for i in iterable: yield i + i -# A generator creates values on the fly. -# Instead of generating and returning all values at once it creates one in each -# iteration. This means values bigger than 15 wont be processed in -# double_numbers. -# We use a trailing underscore in variable names when we want to use a name that -# would normally collide with a python keyword -range_ = range(1, 900000000) -# will double all numbers until a result >=30 found -for i in double_numbers(range_): +# Generators are memory-efficient because they only load the data needed to +# process the next value in the iterable. This allows them to perform +# operations on otherwise prohibitively large value ranges. +# NOTE: `range` replaces `xrange` in Python 3. +for i in double_numbers(range(1, 900000000)): # `range` is a generator. print(i) if i >= 30: break +# Just as you can create a list comprehension, you can create generator +# comprehensions as well. +values = (-x for x in [1,2,3,4,5]) +for x in values: + print(x) # prints -1 -2 -3 -4 -5 to console/terminal + +# You can also cast a generator comprehension directly to a list. +values = (-x for x in [1,2,3,4,5]) +gen_to_list = list(values) +print(gen_to_list) # => [-1, -2, -3, -4, -5] + # Decorators -# in this example beg wraps say -# Beg will call say. If say_please is True then it will change the returned -# message +# In this example `beg` wraps `say`. If say_please is True then it +# will change the returned message. from functools import wraps @@ -698,7 +878,7 @@ 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 :( ``` @@ -715,6 +895,10 @@ print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :( * [A Crash Course in Python for Scientists](http://nbviewer.ipython.org/5920182) * [Python Course](http://www.python-course.eu/index.php) * [First Steps With Python](https://realpython.com/learn/python-first-steps/) +* [A curated list of awesome Python frameworks, libraries and software](https://github.com/vinta/awesome-python) +* [30 Python Language Features and Tricks You May Not Know About](http://sahandsaba.com/thirty-python-language-features-and-tricks-you-may-not-know.html) +* [Official Style Guide for Python](https://www.python.org/dev/peps/pep-0008/) +* [Python 3 Computer Science Circles](http://cscircles.cemc.uwaterloo.ca/) ### Dead Tree |