Python: code specification and naming specification

Machine vision 001 2020-11-13 02:49:36
python code specification naming specification

Python: Code specification and naming convention

All nomenclature rules must abide by these three rules :

1. Names can only be given in letters or _ Start with an underline ;

2. Names cannot contain spaces ;

3. Name cannot overlap with keyword . You can't put the character l( Lowercase letters l),'O''o'( Case letters o)、'I'( Capital I) Used as variable name , Prevention and digital 0、1 confusion .



Modules should be named in lowercase as much as possible , Keep the initials in lowercase , Try not to underline ( Except for multiple words , And a small number of cases ).

# Correct module name
import decoder
import html_decoder
# Module name not recommended
import Decoder


Class name

Class names use humps (CamelCase) Naming style , title case , Private classes can start with an underscore .

class Farm():
class AnimalFarm(Farm):
class _PrivateFarm(Farm):

Put related classes and top-level functions in the same module . Unlike Java, There's no need to limit a class to a module .



All function names are lowercase , If there are more than one word , Separate... With underscores .

def func():
def func_with_env():

Private functions place an underline before the function _.

class Person():
def _private_func():



Try to lower the variable name , If there are more than one word , Separate... With underscores .

Private class members are identified with a single underscore prefix .

Variable names should not have type information , Such as num_list,ani_dict etc. .

if __name__ == '__main__':
count = 0
your_name = ''



Constants are in uppercase , If there are more than one word , Use an underline to separate .


abnormal ExceptionName

With Error As a suffix :

except ValueError as result:

The leading suffix underline indicates

  • A leading underline : Non public
  • One suffix underline : Avoid keyword conflicts
  • Two leading underscores : Use when naming a class property causes name conflicts
  • Two leading and suffix underscores : An object or property that has a special purpose , for example __init__ and __str__



  • In the absence of special circumstances , All documents are in use UTF-8 code ;
  • In the absence of special circumstances , The header of the file must be added with #-*-coding:utf-8-*- identification .


Code format


Unified use 4 Space to indent

Line width

Try not to exceed... Per line of code 80 Characters ( In special cases, it can be slightly more than 80 , But not more than 120).

reason :

  • This is looking at side-by-side Of diff It's very helpful
  • Easy to view code under the console
  • Too long may be a design defect


In short , Natural language use “ Double quotes ”, The machine label uses “ Single quotation marks ”, So most of the code should use “ Single quotation marks ”.

  • Natural language : Use double quotes  "..."
    E.g. error message ; A lot of things are still unicode, Use u" Hello world "
  • Machine identification : Use single quotes  '...'
    for example dict Inside key
  • Regular expressions : Use native double quotes  r"..."
  • docstring (docstring)  Use three double quotes  """......"""

Blank line

  • There are two empty lines between module level functions and class definitions ;
  • Empty line between class member functions ;
  • Multiple empty lines can be used to separate groups of related functions
  • Function can use empty lines to separate out logically related code
class Class:
def __init__(self):
def hello(self):
def main():


import sentence

import Sentences should be written separately :

# Correct writing
import os
import sys
# It's not recommended
import sys,os
# Correct writing
from subprocess import Popen, PIPE

import The sentence should use  absolute import

# Correct writing
from import Bar
# It's not recommended
from import Bar
  • import The statement should be placed in the head of the file , Module description and docstring after , Before global variables ;
  • import Sentences should be arranged in order , Each group is separated by a blank line
import os
import sys
import msgpack
import zmq
import foo

When importing class definitions of other modules , You can use relative import

from myclass import MyClass

If there is a naming conflict , You can use the namespace

import bar



One space on each side of a binary operator [=,-,+=,==,>,in,is not, and]

# Correct writing
i = i + 1
submitted += 1
x = x * 2 - 1
hypot2 = x * x + y * y
c = (a + b) * (a - b)
# It's not recommended
submitted +=1
x = x*2 - 1
hypot2 = x*x + y*y
c = (a+b) * (a-b)

Function's argument list ,, There should be a space after :

# Correct writing
def complex(real, imag):
# It's not recommended
def complex(real,imag):

Function's argument list , The default value is equal sign without spaces :

# Correct writing
def complex(real, imag=0.0):
# It's not recommended
def complex(real, imag = 0.0):

After the left bracket , Don't add extra space before the right bracket :

# Correct writing
spam(ham[1], {eggs: 2})
# It's not recommended
spam( ham[1], { eggs : 2 } )

Don't leave extra space before the left bracket of the dictionary object :

# Correct writing
dict['key'] = list[index]
# It's not recommended
dict ['key'] = list [index]

Do not use extra spaces for alignment assignment statements :

# Correct writing
x = 1
y = 2
long_variable = 3
# It's not recommended
x = 1
y = 2
long_variable = 3


Line break

Python Support line breaks in brackets . There are two scenarios .

1) The second line is indented to the beginning of the bracket :

foo = long_function_name(var_one, var_two,
var_three, var_four)

2) The second line is indented 4 A space , Applicable to the case where the starting bracket is wrapped :

def long_function_name(
var_one, var_two, var_three,

Use backslash \ Line break , Binary operator + . Wait should appear at the end of the line ; Long strings can also be wrapped in this way :

print 'Hello, '\
'%s %s!' %\
('Harry', 'Potter')

Compound statements are forbidden , That is, a line contains multiple statements :

# Correct writing
# It's not recommended

if/for/while Be sure to change lines :

# Correct writing
if foo == 'blah':
# It's not recommended
if foo == 'blah': do_blash_thing()



docstring The most fundamental two points in the specification of :

  1. All the common modules 、 function 、 class 、 Method , It should be written docstring . Private methods don't have to be , But it should be in def A block comment is provided to illustrate .
  2. docstring The end of """ Should have a monopoly on , Unless docstring There is only one line .
"""Return a foobar
Optional plotz says to frobnicate the bizbaz first.
"""Oneline docstring"""


Block annotation

“#” There is a space after the number one , Paragraphs are separated by blank lines ( Also need to “#” Number ):

# Block annotation
# Block annotation
# Block annotation
# Block annotation 

Line notes

Use at least two spaces to separate the statement , Be careful not to use meaningless comments :

# Correct writing
x = x + 1 # The border is bold by one pixel
# It's not recommended ( Meaningless notes )
x = x + 1 # x Add 1


  • In the key part of the code ( Or something more complicated ), Those who can write notes should write notes as much as possible ;

  • The more important comment section , Use multiple equal signs to separate , Can be more eye-catching , Highlight the importance of .
app = create_app(name, options)
# =====================================
# Do not add... Here get post etc. app Routing behavior !!!
# =====================================
if __name__ == '__main__':

Documentation Comments (Docstring)

As a document Docstring It usually appears in the module head 、 Function and class headers , In this way python Can be passed through the object __doc__ Object to get the document .
Editor and IDE It can also be based on Docstring Give an automatic prompt .

  • Document notes to """ The beginning and the end , The first line doesn't wrap , If there are many lines , The last line must wrap , Here are Google Of docstring Style example :
# -*- coding: utf-8 -*-
"""Example docstrings.
This module demonstrates documentation as specified by the `Google Python
Style Guide`_. Docstrings may extend over multiple lines. Sections are created
with a section header and a colon followed by a block of indented text.
Examples can be given using either the ``Example`` or ``Examples``
sections. Sections support any reStructuredText formatting, including
literal blocks::
$ python
Section breaks are created by resuming unindented text. Section breaks
are also implicitly created anytime a new section starts.

Do not copy the function definition prototype in the document comments , It's a concrete description of its content , Explain specific parameters and return values, etc :

# It's not recommended ( Don't write function prototypes and so on )
def function(a, b):
"""function(a, b) -> list"""
... ...
# Correct writing
def function(a, b):
""" Calculate and return a To b The average of the data in the range """
... ...

For function parameters 、 The description of return value, etc numpy standard , As shown below :

def func(arg1, arg2):
""" Here is a sentence summary of the function ( Such as : Calculate average ).
Here is a detailed description of .
arg1 : int
arg1 Specific description of
arg2 : int
arg2 Specific description of
Return value
Specific description of the return value
otherfunc : Other correlation functions, etc ...
Example use doctest Format , stay `>>>` After the code can be automatically run by the document test tool as a test case
>>> a=[1,2,3]
>>> print [x + 3 for x in a]
[4, 5, 6]
  • Document notes are not limited to Chinese and English , But don't mix Chinese and English ;

  • The longer the document comment, the better , Usually one or two sentences can make the situation clear ;

  • modular 、 Public class 、 Public methods , Be able to write notes on documents , You should try to write document notes .















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