Programmers generally choose names for their variables that are meaningful—they document what the variable is used for.
Variable names can be arbitrarily long. They can contain both letters and numbers, but they have to begin with a letter. It is legal to use uppercase letters, but it is a good idea to begin variable names with a lowercase letter (you’ll see why later).
The underscore character, , can appear in a name. It is often used in names with multiple words, such as my_name or airspeed_of_unladen_swallow
If you give a variable an illegal name, you get a syntax error:
>>> 76trombones = 'big parade'SyntaxError: invalid syntax>>> more@ = 1000000SyntaxError: invalid syntax>>> class = 'Advanced Theoretical Zymurgy'SyntaxError: invalid syntax
76trombones is illegal because it does not begin with a letter. more is illegal because it contains an illegal character, @. But what’s wrong with class?
It turns out that class is one of Python’s keywords. The interpreter uses keywords to recognize the structure of the program, and they cannot be used as variable names.
Python 2 has 31 keywords:
|
and as assert break class continue def |
del elif else except exec finally for |
from global if import in is lambda |
not or pass raise return try |
while with yield |
In Python 3, exec is no longer a keyword, but nonlocal is.
You might want to keep this list handy. If the interpreter complains about one of your variable names and you don’t know why, see if it is on this list.
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