Must-see content for beginners (2)

Must-see content for beginners (2)

1. Variable assignment

Variable assignment in Python does not require a type declaration.
Each variable is created in memory, including the variable's identifier, name, and data.
Each variable must be assigned a value before it is used, and the variable will not be created until the variable is assigned.
The equal sign (=) is used to assign values to variables.
The left side of the equals (=) operator is a variable name, and the right side of the equals (=) operator is the value stored in the variable.

2. Standard data types

The data stored in memory can be of many types.
For example, a person's age can be stored in numbers and his name can be stored in characters.
Python defines some standard types for storing various types of data.
Python has five standard data types:

Numbers

String (string)

List

Tuple (tuple)

Dictionary (dictionary)

3. Python Numbers

Numeric data types are used to store numeric values.
They are immutable data types, which means that changing the numeric data type will allocate a new object.
Python supports four different numeric types:

int (signed integer)
long (long integer [can also represent octal and hexadecimal])
float (floating point)

complex (plural)

4. Python String

A string or string (String) is a string of characters consisting of numbers, letters, and underscores.
Generally recorded as:

    s="a1a2···an"(n>=0) 
  

It is a data type in programming languages that represents text.

Python's string list has 2 value orders:

From left to right, the default index starts from 0, and the maximum range is 1 less than the length of the string
Right-to-left indexing starts from -1 by default, the maximum range is the beginning of the string

If you want to obtain a substring from a string, you can use the variable [head subscript: tail subscript] to intercept the corresponding string, where the subscript starts from 0 and can be a positive number or Negative numbers, the subscript can be empty, which means to get the head or tail.

for example:

    s = 'ilovepython' 
  

The result of s[1:5] is love.

When using a colon-separated string, python returns a new object containing the contiguous content identified by the pair of offsets, starting on the left and including the lower bound.

The above result includes the value l of s[1], and the maximum range obtained does not include the upper boundary, which is the value p of s[5].

The plus sign (+) is the string concatenation operator, and the asterisk (*) is the repeat operation. The following example:

Example (Python 2.0+)

 
    #!/usr/bin/python 
     
    # -*- coding: UTF-8 -*-  
    str = ' Hello World! ' print str # Print the complete string
      
    print  
    str [ 0 ] # print the first character in the string
      
    print  
    str [ 2 : 5 ] # prints the third to fifth strings in the string
      
    print  
    str [ 2 : ] # print the string starting at the third character
      
    print  
    str * 2 # print the string twice
      
    print 
      
    str 
     +  
    " 
    TEST 
    " 
      
    # 输出连接的字符串

以上实例输出结果：

Hello World!
H
llo
llo World!
Hello World!Hello World!
Hello World!TEST

Must-see content for beginners (2)

Example (Python 2.0+)

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