How to read in floats from a file?

Question

How can I open a file and read in the floats from the file, when it is in string format, in Python? I would also like to change the values of the each float and rewrite the file over with the new values.

Solution 1

Assuming there's one float per line:

with open("myfile") as f:
    floats = map(float, f)

# change floats

with open("myfile", "w") as f:
    f.write("\n".join(map(str, floats)))

If you want more control with formatting, use the format method of string. For instance, this will only print 3 digits after each period:

    f.write("\n".join(map("{0:.3f}".format, floats)))

Solution 2

The "float()" function accepts strings as input and converts them into floats.

>>> float("123.456")
123.456

Solution 3

def get_numbers():
    with open("yourfile.txt") as input_file:
        for line in input_file:
            line = line.strip()
            for number in line.split():
                yield float(number)

Then just write them back when your done

and as a shorter version (not tested, written from head)

with open("yourfile.txt") as input_file:
    numbers = (float(number) for number in (line for line in (line.split() for line in input_file)))