Take a piece of code as an example QuickStart Python2.7

Invented by Guido Van Rossum in the early 90 's, Python is one of the most popular programming languages, because of its clear and concise syntax I fell in love with Python, whose code is basically executable pseudo-code.

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Note: This article is intended for Python 2.7, but should be suitable for Python 2.x. Soon I will also write such an article for Python 3!

# single comment Start with a well character "" "We can use three double quotation marks (") or single quotation marks (') to write a multiline comment "" "############################################################ 1. Basic data types and Operators ########################################################## # number 3 #=> 3 # You envision mathematical operations 1 + 1 #=> 28-1 #=> 7 Ten * 2 #=> 2035/5 #=> 7 # Division slightly strange. Dividing integers automatically takes the largest integer less than the result 11/4 #=> 2 # and floating-point and floating-point division (the divisor and the dividend are at least one floating-point number, the result will be floating-point numbers) 2.0 # This is a floating-point number 5.0/2.0 #=> 2.5 ... Syntax more explicit # use parentheses to force precedence (1 + 3) * 2 #=> 8 # Boolean is also basic type data TrueFalse # Use not to negate not true #=> falsenot False #=> true # equality ratio Use ==1 = = 1 #=> True2 = 1 #=> False # Unequal comparison using!=1! = 1 #=> False2! = 1 #=> True # More ways to compare 1 < #=> true 1 > #=> False2 <= 2 #=> True2 >= 2 #=> True # Comparison operation can be threaded! 1 < 2 < 3 #=> True2 < 3 < 2 #=> False # You can use the "or ' Create string" This is a string. "' This is also a string. ' # strings can also be added! "Hello" + "world!" #=> "Hello world!" # string can be viewed as a character list "This is a string" [0] #=> ' T ' # none is an object none #=> None # # # ################################################### 2. Variable and Data container #################################################### # printout is very simple print "I ' m Python. Nice to meet you! "# does not need to declare a variable before Some_var = 5 # convention Using Lowercase _ letters _ and _ underscore naming method Some_var #=> 5 # Accessing a variable that was not assigned before will result in an exception try:some_othe R_varexcept Nameerror:print "raises a name error" # assignment can use conditional expression Some_var = A If a > b else b# if A is greater than B, assign a to some_var,# Otherwise, assign B to the Some_var # list to store the data series Li = []# You can start with a pre-populated list other_li = [4, 5, 6] # Use Append to add data to the end of the list li.append (1) #li现在为 [1]li.appe nd (2) #li现在为 [1, 2]li.append (4) #li现在为 [1, 2, 4]li.append (3) #li现在为 [1, 2, 4, 3] # use POP to delete data from the end of the list Li.pop () #=> 3,li is now [ 1, 2, 4]# Save the data just deleted Li.append (3) # now Li again for [1, 2, 4, 3] # access the list like an array li[0] #=> # See the last element Li[-1] #=> 3 # Cross-border access generates a Indexerrortry:li[4] # throws a Indexerror exception except Indexerror:print "raises an Indexerror" # You can view the data of a range in the list by using the Shard (slice) syntax to Mathematically, this is a closed/open interval li[1:3] #=> [2, 4]# omit end position li[2:] #=> [4, 3]# omit start position li[:3] #=> [1, 2, 4] # use Del to remove any element from the list del Li [2] #li现在为 [1, 2, 3] # list can add Li + other_lI #=> [1, 3, 3, 4, 5, 6]-note: Li and Other_li did not change # to link the list with extend Li.extend (other_li) # now Li is [1, 2, 3, 4, 5, 6] # in to detect if the list There is an element 1 in Li #=> True # with the Len function to detect the list length Len (li) #=> 6 # tuple-like list, but immutable tup = (1, 2, 3) tup[0] #=> 1try:tup[0] = 3 # throws a  A TypeError exception except typeerror:print "tuples cannot be mutated." # You can use and list the same operations on tuples Len (tup) #=> 3tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6) Tup[:2] #=> (1, 2) 2 in Tup #=> True # You can unpack tuples into variables A, b, C = (1, 2, 3) # now a equals 1,b equals 2,c equals 3# If you omit parentheses, the default It will also create tuples D, E, F = 4, 5, 6# see how simple E, d = d, e #现在d为5, and E for 4 # Dictionary store mappings for two variable interchange values empty_dict = {}# This is a pre-populated dictionary filled_dict = {"One" : 1, "one": 2, "three": 3} # Look for values in [] syntax filled_dict[' one '] #=> 1 # Get all the keys in a list Filled_dict.keys () #=> ["Three", "one", " One "]# note-the Order of the Dictionary keys is indeterminate # Your results may not match the above output # in to detect if a key exists in the dictionary" one "in the Filled_dict #=> True1 in filled_dict #=> fals E # Attempting to use a nonexistent key throws a Keyerror exception filled_dict[' Four ' #=> throws a Keyerror exception # Use the Get method to avoid Keyerrorfilled_dict.get ("one") #= > 1filled_dict.get ("four") #= = None # The Get method supports a default parameter that returns the default parameter value when there is no key filled_dict.get ("one", 4) #=> 1filled_dict.get ("Four", 4) #=> 4 # Setdefa The Ult method is a safe way to add a new key-value pair to the dictionary Filled_dict.setdefault ("Five", 5) #filled_dict ["Five"] set to 5filled_dict.setdefault ("five",  6) #filled_dict ["Five"] is still 5 # set empty_set = set () # Initializes a collection with several values Filled_set = set ([1, 2, 2, 3, 4]) # Filled_set is now set ([1, 2, 3, 4, 5]) # Perform set intersection operation with & other_set = Set ([3, 4, 5, 6]) Filled_set & Other_set #=> Set ([3, 4, 5]) # to | perform set merge operation Filled_set | Other_set #=> Set ([1, 2, 3, 4, 5, 6]) # with-Performs set difference operation set ([1, 2, 3, 4])-Set ([2, 3, 5]) #=> set ([1, 4]) # in to detect if there is a The value 2 in Filled_set #=> True10 in Filled_set #=> False ###################################################### 3. Control Flow #################################################### # Create a variable Some_var = 5 # The following is an if statement. Indenting is significant in Python. # print "Some_var is smaller than" if Some_var > 10:print "Some_var is totally bigger than 10." Elif Some_var < 10:print "Some_var is smaller than 10." Else:print "SomE_var is indeed 10. " The For loop iterates over the list output: Dog is a mammal cat is a mammal mouse are a mammal "" "for Animal in [" Dog "," cat "," Mouse "]: # You can use% to interpolate The fill format string print '%s is a mammal '% animal "" "while loop until a condition is not met.  Output: 0 1 2 3 "" "x = 0while x < 4:print x + = 1 # x = x + 1 A shorthand # Use try/except block to handle exceptions # valid try for Python 2.6 and later: # Use raise to throw an error raise the Indexerror ("This is a index error") except Indexerror as E:pass # Pass is nothing to do.  Usually used here to do some recovery work # for Python 2.7 and below valid Try:raise Indexerror ("This is an index error") except Indexerror, E: # no "as", comma substitution Pass ###################################################### 4.  function #################################################### # using DEF to create a new function def add (x, y): print "x is%s and y is%s"% (x, y) return x + y # Returns a value with a return statement # call the function with a parameter add (5, 6) #=> 11 and Output "X is 5 and y is 6" # Another way to call a function is the keyword argument add (x=5, y=6) # keyword Parameters can be entered in any order # can define a function that accepts a variable number of positional parameters def varargs (*args): Return args varargs (1, 2, 3) #=> (1, 2, 3) # You can also define a function def that accepts a variable number of keyword arguments Keyword_args (**kwarGS): Return Kwargs # Call this function to see what happens Keyword_args (big= "foot", loch= "ness") #=> {"Big": "foo", "Loch": "Ness"} # can also be accepted at once Two parameters def All_the_args (*args, **kwargs): Print args print Kwargs "" "All_the_args (1, 2, a=3, b=4) output: [1, 2] {" A ": 3," B ": 4} "" "# can also be used when calling a function * and **args = (1, 2, 3, 4) Kwargs = {" A ": 3," B ": 4}foo (*args) #等价于foo (1, 2, 3, 4) foo (**kwargs) # equivalent to Foo (A=3, b=4) foo (*args, **kwargs) # equivalent to Foo (1, 2, 3, 4, A=3, b=4) # Python function is a one-class function Def create_adder (x): def adder (y): Retu RN x + y return adder add_10 = Create_adder (Ten) add_10 (3) #=> 13 # There are also anonymous functions (Lamda x:x > 2) (3) #=> True # There are some built-in high-order letters Number of maps (ADD_10, [1, 2, 3]) #=> [One, A, 13]filter (Lamda x:x > 5, [3, 4, 5, 6, 7]) #=>[6, 7] # You can use list inference to implement mappings and filtering [add_ Ten (i) for i in [1, 2, 3]] #=> [One, a, 13][x for x in [3, 4, 5, 6,7] if x > 5] #=> [6, 7] ###################### ################################ 5. Class #################################################### # Creates a subclass that inherits from object to get a class Human (object): # Class Property. In this class ofShared species = "H. sapiens" # For all samples # Basic initialization construction Method Def __init__ (self, name): # assigns a parameter to the instance's Name property Self.name = name # instance Party Method. All example methods have self as the first parameter def say (self, msg): Return "%s:%s"% (Self.name, msg) # class method is shared by all instances # to invoke the class to invoke the first argument @classmeth  Od def get_species (CLS): Return Cls.species # A call to a static method does not require a reference to a class or instance @staticmethod def grunt (): Return "*grunt*" # Instantiate a Class I = Human (name= "Ian") Print I.say ("HI") # output "Ian:hi" J = Human ("Joel") print J.say ("hello") # output "Joel:hello" # Call class Method I.get_species () #=> "H. sapiens" # Modify the Share property Human.species = "H. Neanderthalensis" I.get_species () #=> "H. neander Thalensis "j.get_species () #=>" H. neanderthalensis "# Call static method Human.grunt () #=>" *grunt* "{% endhighlight%}

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