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Variables and Assignment Style Notes

Spaces are used sparingly in Python. It is common to put spaces around the assignment operator. The recommended style is

c = (f-32)*5/9

Do not take great pains to line up assignment operators vertically. The following has too much space, and is hard to read, even though it is fussily aligned.

a                     = 12
b                     = a*math.log(a)
aVeryLongVariable     = 26
d                     = 13

This is considered poor form because Python takes a lot of its look from natural languages and mathematics. This kind of horizontal whitespace is hard to follow: it can get difficult to be sure which expression lines up with which variable. Python programs are meant to be reasonably compact, more like reading a short narrative paragraph or short mathematical formula than reading a page-sized UML diagram.

Variable names are often given as mixedCase; variable names typically begin with lower-case letters. The lower_case_with_underscores style is also used, but is less popular.

In addition, the following special forms using leading or trailing underscores are recognized:

  • single_trailing_underscore_: used to avoid conflicts with Python keywords. For example: print_ = 42

  • __double_leading_and_trailing_underscore__: used for special objects or attributes, e.g. __init__, __dict__ or __file__. These names are reserved; do not use names like these in your programs unless you specifically mean a particular built-in feature of Python.

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