Take a piece of code as an example to get started with Python2.7 and python2.7

Take a piece of code as an example to get started with Python2.7 and python2.7

Python was invented by Guido Van rosum in the early 1990s s and is currently one of the most popular programming languages. I fell in love with Python because of its clear and concise syntax, the code is basically executable pseudocode.

Welcome! You can contact me via Twitter @ louiedinh or louiedinh AT gmail.

Note: This article focuses on Python 2.7, but it should be applicable to Python 2. x. Soon I will write such an article for Python 3!

# Single line comment starts with a well character ". We can use three double quotation marks (") or single quotation marks (') to compile multi-line comments """################################ ########################## 1. basic data types and operators ################################### ####################### number 3 ##> 3 # The expected mathematical operations 1 + 1 # => 28-1 # => 710*2 # => 2035/5 # => 7 # division is slightly odd. The integer division will automatically take down the largest integer less than the result 11/4 #=> 2 # There are floating point and floating point Division) 2.0 # This is a floating point number 5.0/2.0 #=> 2.5 amount... more explicit syntax # use parentheses to force priority (1 + 3) * 2 #=> 8 # Boolean value is also basic data TrueFalse # Use not to reverse not True #=> Falsenot False #=> True # equal comparison = 1 = 1 #=> True2 = 1 #=> False # Not equal! = 1! = 1 # => False2! = 1 #=> True # more comparison methods 1 <10 #=> True1> 10 #=> False2 <= 2 #=> True2> = 2 #=> True # comparison operations can be concatenated! 1 <2 <3 # => True2 <3 <2 # => False # You can use "or" create string "This is a string. "'This is also a string. '# strings can also be added! "Hello" + "world! "# =>" Hello world! "# A string can be considered as a character list" This is a string "[0] #=> 'T' # None is an object None #=> None ###### ######################################## ####### 2. variables and data containers #################################### ################ print output is very simple print "I'm Python. nice to meet you! "# VARIABLES some_var = 5 need not be declared before the value assignment # The naming conventions for lowercase _ letters _ and _ underscores are used in some_var #=> 5 # An exception occurs when a variable that has not been assigned a value is accessed. try: some_other_var1_t NameError: print "Raises a name error" # When assigning values, you can use the 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 some_var # list used to store the data sequence li = [] # You can start with a pre-filled list other_li = [4, 5, 6] # Use append to add data to the end of the list. 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 It is now [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 deleted data back to li. append (3) # Now li is [1, 2, 4, 3] # access list li [0] #=> 1 # Look at the last element li [-1] #=> 3 # An IndexErrortry is generated for cross-border access: li [4] # throw an IndexError exception; t IndexError: print "Raises an IndexError" # You can use the slice syntax to view the data in a certain range in the list # from a mathematical perspective, this is a closed/open room li [] #=> [2, 4] # omitting the end position li [2:] #=> [4, 3] # omit the starting position li [: 3] #=> [1, 2, 4] # Use del to delete any element del l from the list I [2] # li is now [1, 2, 3] # The list can be added with li + other_li # => [1, 3, 3, 4, 5, 6]-Note: li and other_li have not changed # Use extend to link the list of li. extend (other_li) # Now li is [1, 2, 3, 4, 5, 6] # Use in to check whether an element 1 in li # => True # Use len function to check the list length len (li) #=> 6 # tuples are similar to the list, but cannot be changed. tup = (1, 2, 3) tup [0] #=> 1try: tup [0] = 3 # Throw A TypeError exception when T TypeError: print "Tuples cannot be mutated. "# the same operation len (tup) as the list can be used on tuples #=> 3tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6) tup [: 2] # => (1, 2) 2 in tup # => True # You can unpack tuples to variables a, B, c = (1, 2, 3) # Now a is equal to 1, B is equal to 2, c is equal to 3 # If you omit parentheses, The tuples d, e, f = 4, 5 will be created by default, 6 # Check how simple the values of the two variables are: e, d = d, e # d is 5, e is 4 # dictionary storage ing relationship empty_dict ={}# This is a pre-filled dictionary filled_dict = {"one": 1, "two": 2, "three ": 3} # search for the value filled_dict ['one'] #=> 1 # obtain all the keys in the form of a list. filled_dict.keys () #=> ["three ", "two", "one"] # Note-the sequence of dictionary keys is uncertain # Your results may be inconsistent with the above output results # Use in to check whether a dictionary exists Key "one" in filled_dict # => True1 in filled_dict # => False # If you try to use a key that does not exist, a KeyError is thrown. filled_dict ['four '] # => A KeyError is thrown. # Use the get method to avoid KeyErrorfilled_dict.get ("one ") #=> 1filled_dict.get ("four") #=> None # The get method supports a default parameter. If a key does not exist, filled_dict.get ("one", 4) is returned) #=> 1filled_dict.get ("four", 4) #=> 4 # The setdefault method is a secure way to add a new key-value pair to the dictionary filled_dict.setdefault ("five ", 5) # Set filled_dict ["five"] To 5filled_dict.. Setdefault ("five", 6) # filled_dict ["five"] is still 5 # set empty_set = set () # initialize a set filled_set = set ([1, 2, 2, 3, 4]) # filled_set is now set ([1, 2, 3, 4, 5]) # Use & to execute the set intersection operation other_set = set ([3, 4, 5, 6]) filled_set & other_set # => set ([3, 4, 5]) # Run | execute a set and calculate filled_set | other_set # => set ([1, 2, 3, 4, 5, 6]) # Run the set difference operation set ([1, 2, 3, 4])-set ([2, 3, 5]) # => set ([1, 4]) # Use in to check whether a value of 2 in filled_set exists in the set # => True10 I N filled_set #=> False ################################## #################### 3. control Process ###################################### ############## create a variable some_var = 5 # The following is an if statement. Indentation is important in Python. # Print "some_var is smaller than 10" 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. "For loop iteration output on the list: dog is a mammal cat is a mammal mouse is a mammal" for animal in ["dog", "cat ", "mouse"]: # You can use % to interpolation and format the print string "% s is a mammal" % animal "while loop until a condition is not met. Output: 0 1 2 3 "x = 0 while x <4: print x + = 1 # A shorthand for x = x + 1 # Use the try/try t block to handle exceptions # It is effective for Python 2.6 and later versions. try: # Use raise to throw an error: raise IndexError ("This is an index error") failed t IndexError as e: pass # pass means nothing to do. It is usually used for restoration. # For Python 2.7 and earlier versions, try: raise IndexError ("This is an index error") cannot t IndexError, e: # No "", replace pass #################################### ################## 4. function ####################################### ############# use def to create a function def add (x, y): print "x is % s and y is % s" % (x, y) return x + y # return value using a return statement # Call the add (5, 6) function with Parameters) #=> 11 and output "x is 5 and y is 6" # Another way to call a function is to use the keyword parameter. Dd (x = 5, y = 6) # keyword parameters can be input in any order # You can define the function def varargs (* args) that accepts variable numbers of location parameters ): return args varargs (1, 2, 3) #=> (1, 2, 3) # You can also define the function def keyword_args (** kwargs) that accepts variable number of keyword parameters ): return kwargs # Call this function to see what happens to keyword_args (big = "foot", loch = "ness") #=>{ "big": "foo ", "loch": "ness"} # either of the following parameters can be accepted at a time: 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} "" # In When calling a function, you can also use * And ** args = (1, 2, 3, 4) kwargs = {"a": 3, "B ": 4} foo (* args) # equivalent to 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) # The Python function is the first-class function 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 (lamda x: x> 2) (3) # => True # There are some built-in high-level functions map (add_10, [1, 2, 3]) # => [11, 12, 13] filter (lamda x: x> 5, [3, 4, 5, 6, 7]) # => [6, 7] # map and Filter Using list derivation [add_10 (I) for I in [1, 2, 3] # => [11, 13, 13] [x for x in [3, 4, 5, 6, 7] if x> 5] #=> [6, 7] ####################################### ################ 5. class ####################################### ############# create a subclass that inherits from the object to obtain a class Human (object): # class attributes. Share species = "H. sapiens "# basic initialization constructor def _ init _ (self, name): # assign a parameter to the instance's name attribute self. name = name # instance method. All sample methods use self as the first parameter def say (self, msg): return "% s: % s" % (self. name, msg) # The class method is shared by all instances # Call @ classmethod def get_species (cls) with the call class as the first parameter: return cls. species # static method calls do not require a class or instance reference @ 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 "# modifying shared attributes Human. species = "H. neandrethalensis "I. get_species () # => "H. neandrethalensis "j. get_species () # => "H. neandrethalensis "# Call the static method Human. grunt () # => "* grunt *" {% endhighlight %}