Convert int to double Python [duplicate]

Question

I can't seem to find the answer to this on this site, though it seems like it would be common enough. I am trying to output a double for the ratio of number of lines in two files.

#Number of lines in each file
inputLines = sum(1 for line in open(current_file))
outputLines = sum(1 for line in open(output_file))

Then get the ratio:

ratio = inputLines/outputLines

But the ratio always seems to be an int and rounds even if I initialize it like:

ratio = 1.0

Thanks.

Answer 1

In python 2, the result of a division of two integers is always a integer. To force a float division, you need to use at least one float in the division:

ratio = float(inputLines)/outputLines

Be careful not to do ratio = float(inputLines/outputLines): although that results in a float, it's one obtained after doing the integer division, so the result will be "wrong" (as in "not what you expect")

In python 3, the integer division behavior was changed, and a division of two integers results in a float. You can also use this functionality in python 2.7, by putting from __future__ import division in the begging of your files.

---

The reason ratio = 1.0 does not work is that types (in python) are a property of values, not variables - in other words, variables don't have types.

a= 1.0 # "a" is a float
a= 1   # "a" is now a integer

Answer 2

Are you using Python 2.x?

Try using

>>> from __future__ import division
>>> ratio = 2/5
0.4

to get a float from a division.

Initializing with ratio = 1.0 doesn't work because with ratio = inputLines/outputLines you are re-assigning the variable to int, no matter what it was before.