Python: How can I read in the characters from a line in a file and convert them to floats and strs, depending on if they are numbers or letters?

Question

I have a file that looks like:

1 1 C C 1.9873 2.347 3.88776

1 2 C Si 4.887 9.009 1.21

I would like to read in the contents of the file, line-by-line. When I only had numbers on the lines I used:

for line in readlines(file):
    data = map(float, line.split)

But this only works when all the elements of line.split are numbers. How can I make it store the letters as strings and the numbers as floats?

Answer 1

$ cat 1.py
def float_or_str(x):
  try:
     return float(x)
  except ValueError:
     return x

line = '1 1 C C 1.9873 2.347 3.88776'
print map(float_or_str, line.split())

$python 1.py
[1.0, 1.0, 'C', 'C', 1.9873, 2.347, 3.88776]

Answer 2

for line in infile:
    data = [x if x.isalpha() else float(x) for x in line.split()]

There will be issues if your data contains fields that are neither alphabetic nor valid floating-point numbers (for example, "A1"). Your data doesn't seem to have these from what you said, but if it does, the try/except approach suggested by Igor would probably suit better.

I would probably use a more generic function that can be given the types to try, however:

def tryconvert(value, *types):
    for t in types:
        try:
            return t(value)
        except (ValueError, TypeError):
            continue
    return value

for line in infile:
    data = [tryconvert(x, int, float) for x in line.split()]

This will convert anything that be converted to an integer to an int , failing that it will try float , and then finally it just gives up and returns the original value, which we know will be a string. (If we didn't know it was a string we could just stick str on the end of our call to tryconvert() .)

Answer 3

您可以使用方法str.isalpha（），str.isalphanum（），str.isdigit来确定您的字符串是否为数字。