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+---
+language: python3
+contributors:
+    - ["Louie Dinh", "http://pythonpracticeprojects.com"]
+    - ["Steven Basart", "http://github.com/xksteven"]
+    - ["Andre Polykanine", "https://github.com/Oire"]
+translators:
+    - ["Geoff Liu", "http://geoffliu.me"]
+filename: learnpython3.py
+---
+
+Python was created by Guido Van Rossum in the early 90's. 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 the other tutorial if you want to learn the old Python 2.7
+
+```python
+
+# 用井字符开头的是单行注释
+
+""" 多行字符串用三个引号
+    包裹，也常被用来做多
+    行注释
+"""
+
+####################################################
+## 1. 原始数据类型和运算符
+####################################################
+
+# 整数
+3  # => 3
+
+# 算术没有什么出乎意料的
+1 + 1  # => 2
+8 - 1  # => 7
+10 * 2  # => 20
+
+# 但是除法例外，会自动转换成浮点数
+35 / 5  # => 7.0
+5 / 3  # => 1.6666666666666667
+
+# 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
+
+# 浮点数的运算结果也是浮点数
+3 * 2.0 # => 6.0
+
+# Modulo operation
+7 % 3 # => 1
+
+# x的y次方
+2**4 # => 16
+
+# 用括号决定优先级
+(1 + 3) * 2  # => 8
+
+# 布尔值
+True
+False
+
+# 用not取非
+not True  # => False
+not False  # => True
+
+# 逻辑运算符，注意and和or都是小写
+True and False #=> False
+False or True #=> True
+
+# 整数也可以是布尔值
+0 and 2 #=> 0
+-5 or 0 #=> -5
+0 == False #=> True
+2 == True #=> False
+1 == True #=> True
+
+# 用==判断相等
+1 == 1  # => True
+2 == 1  # => False
+
+# 用!=判断不等
+1 != 1  # => False
+2 != 1  # => True
+
+# 比较大小
+1 < 10  # => True
+1 > 10  # => False
+2 <= 2  # => True
+2 >= 2  # => True
+
+# 大小比较可以连起来！
+1 < 2 < 3  # => True
+2 < 3 < 2  # => False
+
+# 字符串用单引双引都可以
+"这是个字符串"
+'这也是个字符串'
+
+# 用加好连接字符串
+"Hello " + "world!"  # => "Hello world!"
+
+# A string can be treated like a list of characters
+"This is a string"[0]  # => 'T'
+
+# .format can be used to format strings, like this:
+"{} can be {}".format("strings", "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")
+
+
+# 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 all evaluate to False.
+# All other values are True
+bool(0)  # => False
+bool("")  # => False
+bool([]) #=> False
+bool({}) #=> False
+
+
+####################################################
+## 2. Variables and Collections
+####################################################
+
+# Python has a print function
+print("I'm Python. Nice to meet you!")
+
+# No need to declare variables before assigning to them.
+# 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
+
+# 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.
+# (It's a closed/open range for you mathy types.)
+li[1:3]  # => [2, 4]
+# Omit the beginning
+li[2:]  # => [4, 3]
+# Omit the end
+li[:3]  # => [1, 2, 4]
+# Select every second entry
+li[::2]   # =>[1, 4]
+# Revert the list
+li[::-1]   # => [3, 4, 2, 1]
+# Use any combination of these to make advanced slices
+# li[start:end:step]
+
+# Remove arbitrary elements from a list with "del"
+del li[2]   # li is now [1, 2, 3]
+
+# 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
+
+# You can do all those list thingies 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
+# 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
+
+
+# Dictionaries store mappings
+empty_dict = {}
+# Here is a prefilled dictionary
+filled_dict = {"one": 1, "two": 2, "three": 3}
+
+# Look up values with []
+filled_dict["one"]   # => 1
+
+# Get all keys as a list with "keys()".
+# We need to wrap the call in list() because we are getting back an iterable. 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"]
+
+
+# Get all values as a list 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]
+
+
+# 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
+
+
+# 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}
+
+#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}
+
+# 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}
+
+# 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!
+# 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 a list of numbers
+from zero to the given number
+prints:
+    0
+    1
+    2
+    3
+"""
+for i in range(4):
+    print(i)
+
+"""
+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
+
+# Python offers a fundamental abstraction called the Iterable.
+# An iterable is an object that can be treated as a sequence.
+# The object returned the range function, is an iterable.
+
+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
+
+# 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 by calling the __next__ function.
+our_iterator.__next__()  #=> "one"
+
+# It maintains state as we call __next__.
+our_iterator.__next__()  #=> "two"
+our_iterator.__next__()  #=> "three"
+
+# After the iterator has returned all of its data, it gives you a StopIterator Exception
+our_iterator.__next__() # 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 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)
+
+
+# Function Scope
+x = 5
+
+def setX(num):
+    # Local var x not the same as global variable x
+    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
+
+setX(43)
+setGlobalX(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
+
+# TODO - Fix for iterables
+# There are built-in higher order functions
+map(add_10, [1, 2, 3])   # => [11, 12, 13]
+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]
+
+####################################################
+## 5. Classes
+####################################################
+
+
+# We subclass from object to get a class.
+class Human(object):
+
+    # 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. 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
+
+    # An instance method. All methods take "self" as the first argument
+    def say(self, msg):
+        return "{name}: {message}".format(name=self.name, message=msg)
+
+    # 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*"
+
+
+# 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"
+
+# Call our class method
+i.get_species()   # => "H. sapiens"
+
+# Change the shared attribute
+Human.species = "H. neanderthalensis"
+i.get_species()   # => "H. neanderthalensis"
+j.get_species()   # => "H. neanderthalensis"
+
+# Call the static method
+Human.grunt()   # => "*grunt*"
+
+
+####################################################
+## 6. Modules
+####################################################
+
+# You can import modules
+import math
+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
+
+# 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)
+
+
+####################################################
+## 7. Advanced
+####################################################
+
+# 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.
+# Note range is a generator too. Creating a list 1-900000000 would take lot of
+# time to be made
+# 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_):
+    print(i)
+    if i >= 30:
+        break
+
+
+# Decorators
+# in this example beg wraps say
+# Beg will call 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
+
+* [Learn Python The Hard Way](http://learnpythonthehardway.org/book/)
+* [Dive Into Python](http://www.diveintopython.net/)
+* [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 Module of the Week](http://pymotw.com/3/)
+* [A Crash Course in Python for Scientists](http://nbviewer.ipython.org/5920182)
+
+### Dead Tree
+
+* [Programming Python](http://www.amazon.com/gp/product/0596158106/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596158106&linkCode=as2&tag=homebits04-20)
+* [Dive Into Python](http://www.amazon.com/gp/product/1441413022/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1441413022&linkCode=as2&tag=homebits04-20)
+* [Python Essential Reference](http://www.amazon.com/gp/product/0672329786/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0672329786&linkCode=as2&tag=homebits04-20)
+