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diff --git a/python3.html.markdown b/python3.html.markdown deleted file mode 100644 index 430927a9..00000000 --- a/python3.html.markdown +++ /dev/null @@ -1,1047 +0,0 @@ ---- -language: python3 -contributors: - - ["Louie Dinh", "http://pythonpracticeprojects.com"] - - ["Steven Basart", "http://github.com/xksteven"] - - ["Andre Polykanine", "https://github.com/Oire"] - - ["Zachary Ferguson", "http://github.com/zfergus2"] - - ["evuez", "http://github.com/evuez"] - - ["Rommel Martinez", "https://ebzzry.io"] - - ["Roberto Fernandez Diaz", "https://github.com/robertofd1995"] -filename: learnpython3.py ---- - -Python was created by Guido van Rossum in the early 90s. It is now one of the most popular -languages in existence. I fell in love with Python for its syntactic clarity. It's basically -executable pseudocode. - -Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service] - -Note: This article applies to Python 3 specifically. Check out [here](http://learnxinyminutes.com/docs/python/) if you want to learn the old Python 2.7 - -```python - -# Single line comments start with a number symbol. - -""" Multiline strings can be written - using three "s, and are often used - as documentation. -""" - -#################################################### -## 1. Primitive Datatypes and Operators -#################################################### - -# You have numbers -3 # => 3 - -# Math is what you would expect -1 + 1 # => 2 -8 - 1 # => 7 -10 * 2 # => 20 -35 / 5 # => 7.0 - -# Integer division rounds down for both positive and negative numbers. -5 // 3 # => 1 --5 // 3 # => -2 -5.0 // 3.0 # => 1.0 # works on floats too --5.0 // 3.0 # => -2.0 - -# The result of division is always a float -10.0 / 3 # => 3.3333333333333335 - -# Modulo operation -7 % 3 # => 1 - -# Exponentiation (x**y, x to the yth power) -2**3 # => 8 - -# Enforce precedence with parentheses -(1 + 3) * 2 # => 8 - -# Boolean values are primitives (Note: the capitalization) -True -False - -# negate with not -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 are actually 1 and 0 but with different keywords -True + True # => 2 -True * 8 # => 8 -False - 5 # => -5 - -# Comparison operators look at the numerical value of True and False -0 == False # => True -1 == True # => True -2 == True # => False --5 != False # => True - -# Using boolean logical operators on ints casts them to booleans for evaluation, but their non-cast value is returned -# Don't mix up with bool(ints) and bitwise and/or (&,|) -bool(0) # => False -bool(4) # => True -bool(-6) # => True -0 and 2 # => 0 --5 or 0 # => -5 - -# Equality is == -1 == 1 # => True -2 == 1 # => False - -# Inequality is != -1 != 1 # => False -2 != 1 # => True - -# More comparisons -1 < 10 # => True -1 > 10 # => False -2 <= 2 # => True -2 >= 2 # => True - -# Seeing whether a value is in a range -1 < 2 and 2 < 3 # => True -2 < 3 and 3 < 2 # => False -# Chaining makes this look nicer -1 < 2 < 3 # => True -2 < 3 < 2 # => False - -# (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 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." -'This is also a string.' - -# Strings can be added too! But try not to do this. -"Hello " + "world!" # => "Hello world!" -# String literals (but not variables) can be concatenated without using '+' -"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") # => "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" - -# 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" - -# 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") # => "Strings can be interpolated the old way" - -# You can also format using f-strings or formatted string literals (in Python 3.6+) -name = "Reiko" -f"She said her name is {name}." # => "She said her name is Reiko" -# You can basically put any Python statement inside the braces and it will be output in the string. -f"{name} is {len(name)} characters long." # => "Reiko is 5 characters long." - - -# None is an object -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, 0, and empty strings/lists/dicts/tuples all evaluate to False. -# All other values are True -bool(0) # => False -bool("") # => False -bool([]) # => False -bool({}) # => False -bool(()) # => False - -#################################################### -## 2. Variables and Collections -#################################################### - -# Python has a print function -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 string. -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() - -# There are no declarations, only assignments. -# Convention is to use lower_case_with_underscores -some_var = 5 -some_var # => 5 - -# Accessing a previously unassigned variable is an exception. -# 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 -other_li = [4, 5, 6] - -# Add stuff to the end of a list with append -li.append(1) # li is now [1] -li.append(2) # li is now [1, 2] -li.append(4) # li is now [1, 2, 4] -li.append(3) # li is now [1, 2, 4, 3] -# Remove from the end with pop -li.pop() # => 3 and li is now [1, 2, 4] -# Let's put it back -li.append(3) # li is now [1, 2, 4, 3] again. - -# Access a list like you would any array -li[0] # => 1 -# Look at the last element -li[-1] # => 3 - -# Looking out of bounds is an IndexError -li[4] # Raises an IndexError - -# You can look at ranges with slice syntax. -# The start index is included, the end index is not -# (It's a closed/open range for you mathy types.) -li[1:3] # Return list from index 1 to 3 => [2, 4] -li[2:] # Return list starting from index 2 => [4, 3] -li[:3] # Return list from beginning uptil index 3 => [1, 2, 4] -li[::2] # Return list selecting every second entry => [1, 4] -li[::-1] # Return list in reverse order => [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. - -# Remove arbitrary elements from a list with "del" -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] - -# Concatenate lists with "extend()" -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 - -# Examine the length with "len()" -len(li) # => 6 - - -# Tuples are like lists but are immutable. -tup = (1, 2, 3) -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'> - -# 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 - -# 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 -# 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 # tuple 4, 5, 6 is unpacked into variables d, e and f -# respectively such that d = 4, e = 5 and f = 6 -# Now look how easy it is to swap two values -e, d = d, e # d is now 5 and e is now 4 - - -# Dictionaries store mappings from keys to values -empty_dict = {} -# Here is a prefilled dictionary -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. - -# Look up values with [] -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 - for Python -# versions <3.7, dictionary key ordering is not guaranteed. Your results might -# not match the example below exactly. However, as of Python 3.7, dictionary -# items maintain the order at which they are inserted into the dictionary. -list(filled_dict.keys()) # => ["three", "two", "one"] in Python <3.7 -list(filled_dict.keys()) # => ["one", "two", "three"] in Python 3.7+ - - -# 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] in Python <3.7 -list(filled_dict.values()) # => [1, 2, 3] in Python 3.7+ - -# Check for existence of keys in a dictionary with "in" -"one" in filled_dict # => True -1 in filled_dict # => False - -# Looking up a non-existing key is a KeyError -filled_dict["four"] # KeyError - -# Use "get()" method to avoid the KeyError -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 - -# "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 - -# 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} - -# Similar to keys of a dictionary, elements of a set have to be immutable. -invalid_set = {[1], 1} # => Raises a TypeError: unhashable type: 'list' -valid_set = {(1,), 1} - -# Add one more item to the set -filled_set = some_set -filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} -# Sets do not have duplicate elements -filled_set.add(5) # it remains as before {1, 2, 3, 4, 5} - -# Do set intersection with & -other_set = {3, 4, 5, 6} -filled_set & other_set # => {3, 4, 5} - -# Do set union with | -filled_set | other_set # => {1, 2, 3, 4, 5, 6} - -# Do set difference with - -{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 - - - -#################################################### -## 3. Control Flow and Iterables -#################################################### - -# Let's just make a variable -some_var = 5 - -# Here is an if statement. Indentation is significant in Python! -# Convention is to use four spaces, not tabs. -# This prints "some_var is smaller than 10" -if some_var > 10: - print("some_var is totally bigger than 10.") -elif some_var < 10: # This elif clause is optional. - print("some_var is smaller than 10.") -else: # This is optional too. - print("some_var is indeed 10.") - - -""" -For loops iterate over lists -prints: - dog is a mammal - cat is a mammal - mouse is a mammal -""" -for animal in ["dog", "cat", "mouse"]: - # You can use format() to interpolate formatted strings - print("{} is a mammal".format(animal)) - -""" -"range(number)" returns an iterable of numbers -from zero to the given number -prints: - 0 - 1 - 2 - 3 -""" -for i in range(4): - print(i) - -""" -"range(lower, upper)" returns an iterable of numbers -from the lower number to the upper number -prints: - 4 - 5 - 6 - 7 -""" -for i in range(4, 8): - print(i) - -""" -"range(lower, upper, step)" returns an iterable of numbers -from the lower number to the upper number, while incrementing -by step. If step is not indicated, the default value is 1. -prints: - 4 - 6 -""" -for i in range(4, 8, 2): - print(i) - -""" -To loop over a list, and retrieve both the index and the value of each item in the list -prints: - 0 dog - 1 cat - 2 mouse -""" -list = ["dog", "cat", "mouse"] -for i, value in enumerate(list): - print(i, value) - -""" -While loops go until a condition is no longer met. -prints: - 0 - 1 - 2 - 3 -""" -x = 0 -while x < 4: - print(x) - x += 1 # Shorthand for x = x + 1 - -# Handle exceptions with a try/except block -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. -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 - print("All good!") # Runs only if the code in try raises no exceptions -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 -with open("myfile.txt") as f: - for line in f: - print(line) - -# Writing to a file -contents = {"aa": 12, "bb": 21} -with open("myfile1.txt", "w+") as file: - file.write(str(contents)) # writes a string to a file - -with open("myfile2.txt", "w+") as file: - file.write(json.dumps(contents)) # writes an object to a file - -# Reading from a file -with open('myfile1.txt', "r+") as file: - contents = file.read() # reads a string from a file -print(contents) -# print: {"aa": 12, "bb": 21} - -with open('myfile2.txt', "r+") as file: - contents = json.load(file) # reads a json object from a file -print(contents) -# print: {"aa": 12, "bb": 21} - - -# Python offers a fundamental abstraction called the Iterable. -# An iterable is an object that can be treated as a sequence. -# The object returned by the range function, is an iterable. - -filled_dict = {"one": 1, "two": 2, "three": 3} -our_iterable = filled_dict.keys() -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 - -# However we cannot address elements by index. -our_iterable[1] # Raises a TypeError - -# An iterable is an object that knows how to create an iterator. -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" - -# It maintains state as we iterate. -next(our_iterator) # => "two" -next(our_iterator) # => "three" - -# After the iterator has returned all of its data, it raises a StopIteration exception -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"] - - -#################################################### -## 4. Functions -#################################################### - -# 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 - -# Calling functions with parameters -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. - -# You can define functions that take a variable number of -# positional arguments -def varargs(*args): - return args - -varargs(1, 2, 3) # => (1, 2, 3) - -# You can define functions that take a variable number of -# keyword arguments, as well -def keyword_args(**kwargs): - return kwargs - -# Let's call it to see what happens -keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"} - - -# You can do both at once, if you like -def all_the_args(*args, **kwargs): - print(args) - print(kwargs) -""" -all_the_args(1, 2, a=3, b=4) prints: - (1, 2) - {"a": 3, "b": 4} -""" - -# When calling functions, you can do the opposite of args/kwargs! -# 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 all_the_args(1, 2, 3, 4) -all_the_args(**kwargs) # equivalent to all_the_args(a=3, b=4) -all_the_args(*args, **kwargs) # equivalent to all_the_args(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) - -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. - -# Function Scope -x = 5 - -def set_x(num): - # Local var x not the same as global variable x - x = num # => 43 - print(x) # => 43 - -def set_global_x(num): - global x - print(x) # => 5 - x = num # global var x is now set to 6 - print(x) # => 6 - -set_x(43) -set_global_x(6) - - -# Python has first class functions -def create_adder(x): - def adder(y): - return x + y - return adder - -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 - -# There are built-in higher order functions -list(map(add_10, [1, 2, 3])) # => [11, 12, 13] -list(map(max, [1, 2, 3], [4, 2, 1])) # => [4, 2, 3] - -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] - -# You can construct set and dict comprehensions as well. -{x for x in 'abcddeef' if x not in 'abc'} # => {'d', 'e', 'f'} -{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16} - - -#################################################### -## 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 -# are defined in 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" statement to create a class -class Human: - - # A class attribute. It is shared by all instances of this class - species = "H. sapiens" - - # Basic initializer, this is called when this class is instantiated. - # Note that the double leading and trailing underscores denote objects - # or attributes that are used by Python but that live in user-controlled - # namespaces. Methods(or objects or attributes) like: __init__, __str__, - # __repr__ etc. are called special methods (or sometimes called dunder methods) - # You should not invent such names on your own. - def __init__(self, name): - # 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): - 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 - @classmethod - def get_species(cls): - return cls.species - - # A static method is called without a class or instance reference - @staticmethod - 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. - # There's no need to write trivial getters and setters in Python, though. - @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*" - - # Cannot call static method with instance of object - # because i.grunt() will automatically put "self" (the object i) as an argument - print(i.grunt()) # => TypeError: grunt() takes 0 positional arguments but 1 was given - - # Update the property for this instance - i.age = 42 - # Get the property - i.say(i.age) # => "Ian: 42" - j.say(j.age) # => "Joel: 0" - # Delete the property - del i.age - # i.age # => this would raise an AttributeError - - -#################################################### -## 6.1 Inheritance -#################################################### - -# Inheritance allows new child classes to be defined that inherit methods and -# variables from their parent class. - -# Using the Human class defined above as the base or parent class, we can -# define a child class, Superhero, which inherits the class variables like -# "species", "name", and "age", as well as methods, like "sing" and "grunt" -# from the Human class, but can also have its own unique properties. - -# To take advantage of modularization by file you could place the classes above in their own files, -# say, human.py - -# To import functions from other files use the following format -# from "filename-without-extension" import "function-or-class" - -from human import Human - - -# Specify the parent class(es) as parameters to the class definition -class Superhero(Human): - - # If the child class should inherit all of the parent's definitions without - # any modifications, you can just use the "pass" keyword (and nothing else) - # but in this case it is commented out to allow for a unique child class: - # pass - - # Child classes can override their parents' attributes - species = 'Superhuman' - - # Children automatically inherit their parent class's constructor including - # its arguments, but can also define additional arguments or definitions - # and override its methods such as the class constructor. - # This constructor inherits the "name" argument from the "Human" class and - # adds the "superpower" and "movie" arguments: - def __init__(self, name, movie=False, - superpowers=["super strength", "bulletproofing"]): - - # add additional class attributes: - self.fictional = True - self.movie = movie - # be aware of mutable default values, since defaults are shared - self.superpowers = superpowers - - # The "super" function lets you access the parent class's methods - # that are overridden by the child, in this case, the __init__ method. - # This calls the parent class constructor: - super().__init__(name) - - # override the sing method - def sing(self): - return 'Dun, dun, DUN!' - - # add an additional instance method - def boast(self): - for power in self.superpowers: - print("I wield the power of {pow}!".format(pow=power)) - - -if __name__ == '__main__': - sup = Superhero(name="Tick") - - # Instance type checks - if isinstance(sup, Human): - print('I am human') - if type(sup) is Superhero: - print('I am a superhero') - - # Get the Method Resolution search Order used by both getattr() and super() - # This attribute is dynamic and can be updated - print(Superhero.__mro__) # => (<class '__main__.Superhero'>, - # => <class 'human.Human'>, <class 'object'>) - - # Calls parent method but uses its own class attribute - print(sup.get_species()) # => Superhuman - - # Calls overridden method - print(sup.sing()) # => Dun, dun, DUN! - - # Calls method from Human - sup.say('Spoon') # => Tick: Spoon - - # Call method that exists only in Superhero - sup.boast() # => I wield the power of super strength! - # => I wield the power of bulletproofing! - - # Inherited class attribute - sup.age = 31 - print(sup.age) # => 31 - - # Attribute that only exists within Superhero - print('Am I Oscar eligible? ' + str(sup.movie)) - -#################################################### -## 6.2 Multiple Inheritance -#################################################### - -# Another class definition -# bat.py -class Bat: - - species = 'Baty' - - def __init__(self, can_fly=True): - self.fly = can_fly - - # This class also has a say method - def say(self, msg): - msg = '... ... ...' - return msg - - # And its own method as well - def sonar(self): - return '))) ... (((' - -if __name__ == '__main__': - b = Bat() - print(b.say('hello')) - print(b.fly) - - -# And yet another class definition that inherits from Superhero and Bat -# superhero.py -from superhero import Superhero -from bat import Bat - -# Define Batman as a child that inherits from both Superhero and Bat -class Batman(Superhero, Bat): - - 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". - Superhero.__init__(self, 'anonymous', movie=True, - superpowers=['Wealthy'], *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() - - # 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 'superhero.Superhero'>, - # => <class 'human.Human'>, - # => <class 'bat.Bat'>, <class 'object'>) - - # Calls parent method but uses its own class attribute - print(sup.get_species()) # => Superhuman - - # Calls overridden 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) # => 100 - - # Inherited attribute from 2nd ancestor whose default value was overridden. - print('Can I fly? ' + str(sup.fly)) # => Can I fly? False - - - -#################################################### -## 7. Advanced -#################################################### - -# Generators help you make lazy code. -def double_numbers(iterable): - for i in iterable: - yield i + i - -# 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`. If say_please is True then it -# will change the returned message. -from functools import wraps - - -def beg(target_function): - @wraps(target_function) - def wrapper(*args, **kwargs): - msg, say_please = target_function(*args, **kwargs) - if say_please: - return "{} {}".format(msg, "Please! I am poor :(") - return msg - - return wrapper - - -@beg -def say(say_please=False): - msg = "Can you buy me a beer?" - return msg, say_please - - -print(say()) # Can you buy me a beer? -print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :( -``` - -## Ready For More? - -### Free Online - -* [Automate the Boring Stuff with Python](https://automatetheboringstuff.com) -* [Ideas for Python Projects](http://pythonpracticeprojects.com) -* [The Official Docs](http://docs.python.org/3/) -* [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/) -* [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/) -* [Dive Into Python 3](http://www.diveintopython3.net/index.html) -* [A Crash Course in Python for Scientists](http://nbviewer.jupyter.org/gist/anonymous/5924718) |