Fundamentals of Python special topic grammar

Knowledge seeker 2020-11-13 12:02:45
fundamentals python special topic grammar

One Preface

Knowledge seekers intend to put python The series is finished , Write an article when you have time ;

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Two python Basic grammar

2.1 code

python The default syntax is utf-8 But sometimes when you write Chinese notes, you will report an error , Good habits are in python Add the following sentence at the beginning of the file

# -*- coding: utf-8 -*-

If you want to convert to other encoding , Example

# -*- coding: cp-1252 -*-

2.2 identifier

What we call an identifier is actually a variable

  • The first character must be a letter or underscore in the alphabet _ . Example z_szxz, perhaps _zszxz;
  • The rest of the identifier consists of the letters 、 Numbers and underscores . Example beauty1
  • Identifiers are case sensitive .
  • Identifier cannot be a keyword ; Example defclassFalseTrue etc.

2.3 keyword

Key words are reserved words , It cannot be used as an identifier ; stay python Of IDLE Type the following statements to view reserved words

>>> import keyword
>>> keyword.kwlist


['False', 'None', 'True', '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']

2.4 notes

Single-line comments With # start

# Single-line comments 
print ("Hello, Python!") # You can also write here 

Multiple line comments can use three single quotation marks ''' perhaps Three double quotes """

""" It's a gorgeous dividing line """
print('hello Knowledge seeker ')
''' It's a beautiful dividing line '''
print('hello you')

2.5 Blank lines and indents

stay python In order to make the code more readable , It's usually a sentence, a line , The relationship between the two sides of the operation should be separated by spaces ;

hello = world

python Inside The indent of is not to be used indiscriminately , In general, it is representative of the program ;

such as if Sentence indentation ,

if True:
print (" Stewed goose in an iron pot ")
print (" Go hungry ")

If it is written in the following way, it will report an error , as a result of else There is no sentence body ;

if True:
print (" Stewed goose in an iron pot ")
print (" Go hungry ")


Often see python The string of the statement It means that they are all Single quotation marks , Use less double quotes , In fact, it can be , It is customary to use single quotation marks It will be more professional ; There is also a statement that does not need to end with a seal ;

hello = ' Hello '

2.7 Simple guided packets

stay python use import perhaps from…import To import the corresponding module .

If you import all of a module, use import

import sys

If the day comes, some functions of a module will be used from…import

from sys import argv

2.8 Input and output

python Use in input Function represents input from the console , Program run to input Statement will pause , Then enter the console and press enter to continue the program ;

input(" Please enter :")

python Use in print Function represents the console output ;


2.9 Multi line statement

stay In order to be more readable in a long line of statements , Use \ To separate For multiple lines , The essence is still a sentence ;

color = '555555' + \
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