How to read in one character at a time from a file in python?

Question

I want to read in a list of numbers from a file as chars one char at a time to check what that char is, whether it is a digit, a period, a + or -, an e or E, or some other c

Answer 1

Here is a technique to make a one-character-at-a-time file iterator:

from functools import partial

with open("file.data") as f:
    for char in iter(partial(f.read, 1), ''):
        # now do something interesting with the characters
        ...

• The with-statement opens the file and unconditionally closes it when you're finished.
• The usual way to read one character is f.read(1).
• The partial creates a function of zero arguments by always calling f.read with an argument of 1.
• The two argument form of iter() creates an iterator that loops until you see the empty-string end-of-file marker.

Answer 2

for x in open() reads lines from a file. Read the entire file in as a block of text, then go through each character of the text:

import sys

def is_float(n):
    state = 0
    src = ""
    ch = n
    if state == 0:
        if ch.isdigit():
            src += ch
            state = 1
            ...

data = open("file.data", 'r').read()
for n in data: # characters
    sys.stdout.write("%12.8e\n" % is_float(n))

Answer 3

In fact it's much easier. There is a nice utility in itertools, that's often neglected. ;-)

for character in itertools.chain.from_iterable(open('file.data')):
    process(character)