author：Once Day date:2022 year 2 month 16 Japan
The purpose of this document is to summarize the relevant contents , Scattered knowledge is difficult to remember and learn .
This document is based on windows platform .
View a full range of documents ：python Basics _CSDN Blog .
By default python Use UTF-8 code , In memory unicode character string ,python Will automatically complete the conversion process ！
You can also specify other codes for the source file ：
# -*- coding: GB 2312 -*-
The simplified Chinese coding method is specified above , however Recommended UTF-8 code .
An identifier is a pair of variables 、 Constant 、 function 、 Class and other objects .
python stay Python 3 in , Not ASCII Encoded identifiers are also allowed , Like using Chinese . Here are the naming requirements ：
It is recommended to use identifiers starting with English letters , The beginning of an underscore usually has a meaning .
>>> I love you! python=100
>>> I love you! python
100
You can see python The characters supported by identifiers are quite broad , But this is not recommended , Just a demonstration ！
Be careful python Identifiers cannot contain special characters , Such as ~、@、！、#、$ wait .
Reserved words are keywords , We can't use them as any identifier names .Python The standard library provides a keyword module , We can use it to view all reserved words in the current version ：
>>> import keyword
>>> keyword.kwlist
['False', 'None', 'True', '__peg_parser__', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
There is no need to memorize the keywords here , There is no need to know the full meaning , Because when you use keywords as identifiers, you will be prompted directly for syntax errors ,
>>> and = 1
File "<input>", line 1
and =1
^
SyntaxError: invalid syntax
Annotating code is always a good habit ！
python There is only one comment , namely ：
# The first note
# I'm a one-way note
This comment can only be single line , But there are other ways to keep the code from running . namely ：
""" This is a multiline comment This is a multiline comment """
''' You can also comment multiple lines with three single quotes '''
actually (""") and (’’’) All represent multi line strings , Here the code becomes a string , Naturally, it will not work ！
If you use multiline comments under classes and functions , For example, the following ：
def func(a, b):
""" This is the function documentation . :param a: Addition number :param b: Addition number :return: and """
return a + b
class Foo:
""" This class initializes a age Variable """
def __init__(self, age):
self.age = age
This annotation has a special purpose , Used to __doc__ Provide document content , These contents can be through off the shelf tools , Automatically collect , Form help documents . But the position of this annotation is fixed , As shown above .
in addition , stay linux In the environment , You can use the following comments to determine Python The path of the interpreter ：
#!/usr/bin/env python
# Use... In the system environment variable python
#!/usr/bin/python3
# Use a fixed version of python
.....
This line is annotated on the first line , And it's only useful by directly accessing files , Such as ：
$ ./xxxx.py
Python The most distinctive feature is the use of indentation to represent code blocks . The number of indented spaces is variable , however Statements in the same code block must contain the same number of indented spaces .
sentence ： In the code , Be able to express a meaning completely 、 The shortest code for operation or logic , It's called a statement .
Python Standard statements do not require semicolons or commas to indicate the end of the statement , Simply changing the line means that the statement has ended , The next sentence begins .
# This is a class code block
class Func:
# This is the code block of a function in the class
def __init__(self, x, y):
self.x = x
self.y = y
def get_x(self):
return self.x
A code block is a set of statements linked together to accomplish a particular function . There is judgment 、 loop 、 function 、 Classes and other code blocks .
If the number of spaces indented in the code block is inconsistent , May trigger IndentationError: unexpected indent abnormal .
Here we need to pay attention to tab and space Transformation , Now mature compilers will automatically tab Convert to four spaces ！
Use backslash (\),
>>> string='i like you,'+\
'you just refuse me!'+\
'i am sad....'
>>> string
'i like you,you just refuse me!i am sad....'
Pay attention to [], {}, or () Multiple lines in , You don't need to use backslashes (\), Directly enter , Then write .
>>> print(' I love you! ,'
+' Like flies love cow dung ！')
I love you! , Like flies love cow dung ！
stay Python use import perhaps from…import To import the corresponding module .
The whole module (somemodule) Import , The format is ：import somemodule
Import a function from a module , The format is ：from somemodule import somefunction
Import multiple functions from a module , The format is ：from somemodule import firstfunc, secondfunc, thirdfunc
Import all functions in a module into , The format is ：from somemodule import *
import sys
print('================Python import mode==========================')
print (' The command line arguments are :')
for i in sys.argv:
print (i)
print ('\n python Path is ',sys.path)
# perhaps
from sys import argv,path # Import specific members
print('================python from import===================================')
print('path:',path) # Because it has been imported path member , So there is no need to add sys.path
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