Variables and Assignment Style Notes

Variables and Assignment Style Notes
	Chapter 6. Variables, Assignment and Input

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.


Variable and Assignment Exercises		Chapter 7. Truth, Comparison and Conditional Processing