Naming conventions
Never use l, O, or I single letter names as these can be mistaken for 1 and 0, depending on typeface |
O = 2 # This may look like you're trying to reassign 2 to zero |
Function |
function, my_function |
Variable |
x, var, my_variable |
Class |
Model, MyClass |
Method |
class_method, method |
Constant |
CONSTANT, MY_CONSTANT, MY_LONG_CONSTANT |
Module |
module.py, my_module.py |
Package |
package, mypackage |
Maximum Line Length and Line Breaking
PEP 8 suggests lines should be limited to 79 characters. This is because it allows you to have multiple files open next to one another, while also avoiding line wrapping.
Python will assume line continuation if code is contained within parentheses, brackets, or braces:
def function(arg_one, arg_two,
arg_three, arg_four):
return arg_one
If it is impossible to use implied continuation, then you can use backslashes to break lines instead:
from mypkg import example1, \
example2, example3
# Recommended
total = (first_variable
+ second_variable
- third_variable)
# Not Recommended
total = (first_variable +
second_variable -
third_variable)
|
Identation
Use 4 consecutive spaces to indicate indentation. |
Prefer spaces over tabs. |
Comments
Limit the line length of comments and docstrings to 72 characters. |
Use complete sentences, starting with a capital letter. |
Make sure to update comments if you change your code. |
Block Comments
Indent block comments to the same level as the code they describe. |
Start each line with a # followed by a single space. |
Separate paragraphs by a line containing a single #. |
Inline Comments
Use inline comments sparingly. |
Write inline comments on the same line as the statement they refer to. |
Separate inline comments by two or more spaces from the statement. |
Start inline comments with a # and a single space, like block comments. |
Don’t use them to explain the obvious. |
When to Avoid Adding Whitespace
The most important place to avoid adding whitespace is at the end of a line. This is known as trailing whitespace |
Immediately inside parentheses, brackets, or braces: |
Before a comma, semicolon, or colon: |
Before the open parenthesis that starts the argument list of a function call: |
Before the open bracket that starts an index or slice: |
Between a trailing comma and a closing parenthesis: |
To align assignment operators: |
immediately inside brackets, as well as before commas and colons. |
Programming Recommendations
Don’t compare boolean values to True or False using the equivalence operator. |
Use the fact that empty sequences are falsy in if statements. |
Use is not rather than not ... is in if statements. |
Don’t use if x: when you mean if x is not None: |
Use .startswith() and .endswith() instead of slicing. |
|
|
Code Layout
Surround top-level functions and classes with two blank lines |
Surround method definitions inside classes with a single blank line. |
Use blank lines sparingly inside functions to show clear steps. |
Indentation Following Line Breaks
There are two styles of indentation you can use. |
The first of these is to align the indented block with the opening delimiter: |
An alternative style of indentation following a line break is a hanging indent. This is a typographical term meaning that every line but the first in a paragraph or statement is indented. |
Indentation Following Line Breaks 2
def function(arg_one, arg_two,
arg_three, arg_four):
return arg_one
x = 5
if (x > 3 and
x < 10):
print(x)
x = 5
if (x > 3 and
x < 10):
# Both conditions satisfied
print(x)
x = 5
if (x > 3 and
x < 10):
print(x)
# hanging indent
var = function(
arg_one, arg_two,
arg_three, arg_four)
|
Where to Put the Closing Brace
PEP 8 provides two options for the position of the closing brace in implied line continuations:
1 - Line up the closing brace with the first non-whitespace character of the previous line:
list_of_numbers = [
1, 2, 3,
4, 5, 6,
7, 8, 9
]
2 - Line up the closing brace with the first character of the line that starts the construct:
list_of_numbers = [
1, 2, 3,
4, 5, 6,
7, 8, 9
]
|
Documentation Strings
Surround docstrings with three double quotes on either side, as in """This is a docstring""". |
Write them for all public modules, functions, classes, and methods. |
Put the """ that ends a multiline docstring on a line by itself: |
For one-line docstrings, keep the """ on the same line: |
Whitespace Around Binary Operators
Surround the following binary operators with a single space on either side: |
Assignment operators (=, +=, -=, and so forth) |
Comparisons (==, !=, >, <. >=, <=) and (is, is not, in, not in) |
Booleans (and, not, or) |
When = is used to assign a default value to a function argument, do not surround it with spaces. |
def function(default_parameter=5): |
y = x**2 + 5 |
z = (x+y) * (x-y) |
if x>5 and x%2==0: |
# Treat the colon as the operator with lowest priority |
list[x+1 : x+2] |
In an extended slice, both colons must be surrounded by the same amount of whitespace |
list[3:4:5] |
list[x+1 : x+2 : x+3] |
The space is omitted if a slice parameter is omitted |
list[x+1 : x+2 :] |
When to Ignore PEP 8
If complying with PEP 8 would break compatibility with existing software |
If code surrounding what you’re working on is inconsistent with PEP 8 |
If code needs to remain compatible with older versions of Python |
|
