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Chapter 2. Variables, expressions and statements
For this reason, it is agood idea toaddnotes to your programsto explainin natural
language what the program is doing. These notes are called comments, and they
start with the
#
symbol:
# compute the percentage of the hour that has elapsed
percentage = (minute * 100) / 60
In this case, the comment appears on a line by itself. You can also put comments
at the end of a line:
percentage = (minute * 100) / 60
# percentage of an hour
Everything from the
#
to the end of the line is ignored—it has no effect on the
program.
Comments aremost useful when they document non-obvious features of the code.
It is reasonable to assume that the reader can figure out what the code does; it is
much more useful to explain why.
This comment is redundant with the code and useless:
v = 5
# assign 5 to v
This comment contains useful information that is not in the code:
v = 5
# velocity in meters/second.
Goodvariable namescan reduce theneedfor comments, but longnames can make
complex expressions hard to read, so there is a tradeoff.
2.12 Choosing mnemonic variable names
As long as you follow the simple rules of variable naming, and avoid reserved
words, you have a lot of choice when you name your variables. In the beginning,
this choice can be confusing both when you read a program and when you write
your own programs. For example, the following three programs are identical in
terms of what they accomplish, but very different when you read them and try to
understandthem.
a = 35.0
b = 12.50
c = a * b
print c
hours = 35.0
rate = 12.50
pay = hours * rate
print pay
x1q3z9ahd = 35.0
x1q3z9afd = 12.50
x1q3p9afd = x1q3z9ahd * x1q3z9afd
print x1q3p9afd
