Basic Python knowledge (3): Basic python knowledge

Basic Python knowledge (3): Basic python knowledge
I. Functions

Def function name (): Code encapsulated by the function...

• Def is short for define
• Other Python files can be introduced and called.
• DefinitionAnd other code including comments keep two blank lines

PycharmDebuggingHour

　　　　NotePress Ctrl + Q to view the function description.

Ii. Modules

A module is a core concept of Python program architecture.

• The module is like a toolkit and needs to be imported. import this module.
• Each Python source code file ending with. py is a module.
• The complete set variables and functions defined in the module are tools that can be directly used by the module.

Usage: (easy to reuse code that has been written)

(Popular Science) pyc file-optimization of startup speed

First, compile the import module into a bytecode file and put it in the _ pycache _ directory.

Iii. Advanced variable types

First, Mark that all non-numeric variables in Python support the following features:

1. List (the most frequently used data type ("array") | data of the same type is usually stored)

• Used to store a string of information
• The list is defined by [], and data is separated
• Its Index starts from 0.

Common Operations: (. Press the tab key to view details)

(1) Increase

(2) Delete

Del keyword (delete) delete list elements (Popular Science)

In essence, a variable is deleted from the memory, that is, it cannot be used any more.

(3) Data Statistics (4) sorting (5) loop Traversal

A for loop can traverse all non-numeric variables: List, tuples, dictionaries, and strings.

for name in name_list:　　print(name)

 

2. Tuple (elements cannot be modified | used to store different types of data)

• Tuples represent a sequence composed of multiple elements.
• Users store a string of Information separated by commas (,).
• Defined ()
• The index also starts from 0.
  • Create null tuple = ()
  • Name of the value tuples corresponding to the index [0]
  • The tuples only contain one element. You must add a comma (,) to the end of the element.

Common Operations: (. Press the tab key to view details)

Application scenarios

• • Conversion between tuples and lists
    • List (tuples) tuples --> list
    • Tuple (list) list --> tuples

3. dictionary (the most flexible data types in Python except the list)

• You can also store multiple data.
  • It is usually used to store information about an object.
• Differences from List
  • A list is a set of ordered objects.
  • A dictionary is a collection of unordered objects.
• Dictionary defined {}
• The dictionary uses key-value pairs to store data and key-value pairs for separation.
  • The key is the index.
  • Value is Data
  • Use: To separate keys and values
  • The key must be unique.
  • Values can be of any data type, but keys can only use strings, numbers, or tuples.

Common Operations: (. Press the tab key to view details)

 

Other operations

Loop Traversal  Application scenarios4. String (the data type of text information)

• One pair of double quotes or one pair of single quotes can be used to define a string ("to define a string in most programming languages)
  • Flexible Use
• Use the index to obtain the characters at the corresponding position, also starting from 0
• You can use for loop Traversal

Common Operations: (. Press the tab key to view details)

• (1) 9 types of judgment
• (2) search and replace 7 types

• (3) case-insensitive Conversion
• (4) three types of text alignment
• (5) Remove three types of white space characters
• (6) splitting and connection 5 types

String slices (applicable to strings, lists, and meta groups)

• Use the index value to define the range and cut a small set from a large set.
• A dictionary is an unordered set that uses key-value pairs to store data.

String [start index: End index: Step Size]

 

Skip slice

You just want to end the index at the end of the string without writing it.

Try some examples ~

Num_str = "0123456789"

• (1), num_str [2: 6]
• (2), num_str [2:]
• (3), num_str [0: 6]/num_str [: 6]
• (4), num_str [:]
• (5), num_str [: 2]
• (6), num_str [1: 2]
• (7), num_str [2:-1] (-1 is truncated to the last one)
• (8), num_str [-2:]
• (9), num_str [:-1] (step-1 is Left tangent)