Readability

A well written program should not only be efficient and correct, but it should also be easy to read. While Python is very flexible in terms of program and code structure, good use syntax, stylistics elements, and white space can help make your code more readable and easier to comprehend. Remember, just because the syntax of the language allows you to do something, doesn't mean it's the best choice to employ when attempting to create a well structured program.

Spacing
Long Lines
Wrapping Statements

Spacing

Horizontal Spacing. Horizontal spacing within statements can help to make your code easier to read, especially when printed in a small font size.

Most basic Python symbols used in constructing expressions should have at least one space before and one space after each.

x = y * z + 50 - x
isValid = x >= 0 and x < 100

Notable exceptions include parentheses and operators comprised of multiple symbols (e.g., +=, <=).

Vertical Spacing. Blank lines should be used to separate long, logically related blocks of code. To be effective, blank lines should be used consistently. Specifically:

The file header comment should be separated from the remaining source code by at least one blank line.
The end of a statement block should be separated from the next statement by at least one blank line.
Within a long piece of code, groups of related statements may be separated from other groups of the next statement by a blank line. Typically such blocks would be preceded by an inline comment.
Multiple functions should be separated by at least one blank line as should methods within a class definition.

Long Lines

While it may be easy to read your source file within the text editor or IDE, remember that in many cases, your source code will be viewed from printed copy of the text file. In this case, the long lines have to be wrapped in order for them to fit on the page. This can produce ugly and distracting results.

Long lines (those with more than 75 characters) should be manually wrapped. This includes both statements and comments.
In the Wing IDE, the vertical red line provides a visual aide to remind you to wrap long lines. Unless you have changed the default value, the vertical line represents text column 80.

Wrapping Lines

When a statement is wrapped, the part continued on the next line should be indented and aligned, if possible, with the previous statement. For example, consider the long expression in the example below and notice how the continued part is indented and aligned with the first part of the expression.

result = (self._value1 * self._value2 + anotherValue) \
* self._numberOfValues

If a string (other than the triple quotes version) is too long to fit on one line, it should be manually wrapped using the backslash between separate strings. Do not use the backslash within a string literal. The example below shows how to correctly wrap long literal strings.

myString = "this is a long"\
" string wrapped across 2 lines."

If a logical expression must be split across more than one line, it should be wrapped such that the expression is easy to follow. It should never be split between a relational operator, but it can be split between a boolean operator. For example,

if amount <= amountRequired and \
amountOwed > 0.0 :

If an assertion or exception statement must be wrapped, the string containing the message should fit on a single line and not split across multiple lines. For example,

assert value > 0 and node is not None, \
"The value must be > 0 and the list can not be empty."

Comments

Python Style Guide

Storage Classes