Variable Names and Keywords¶

Variable names can be arbitrarily long.
They can contain both letters and digits, but they have to begin with a letter or an underscore.
Although it is legal to use uppercase letters, by convention we don’t.
Case matters. Bruce and bruce are different variables.
The underscore character ( _) can appear in a name (often used in names with multiple words, such as my_name or price_of_tea_in_china).
A safe rule for beginners is to start all names with a letter.

If you give a variable an illegal name, you get a syntax error:

76trombones = "big parade"
more$ = 1000000
class = "Computer Science 101"
print(76trombones)
print(more$)
print(class)

(wrongassignment)

76trombones is illegal because it does not begin with a letter.
more$ is illegal because it contains an illegal character, the dollar sign.
But what’s wrong with class? class is one of the Python keywords.

Keywords define the language’s syntax rules and structure, and they cannot be used as variable names.

Python has thirty-something keywords:

and	as	assert	break	class	continue
def	del	elif	else	except	exec
finally	for	from	global	if	import
in	is	lambda	nonlocal	not	or
pass	raise	return	try	while	with
yield	True	False	None

Programmers generally choose names for their variables that are meaningful to the human readers of the program to remember what the variable is used for.