仅当行不是全部以空格开头时，才返回true

Question

lines = files.readlines()

for line in lines:
    if not line.startswith(' '):
        res = True
    if line.startswith(' '):
        res = False
return res

This is my code, however, it returns True for at least one line is not starting with space. How do I fix it so it will return True if only if every line in the file I opened starts with something other than space. If at least one line starts with a space then return False.

Answer 1

Use all() :

Demo:

>>> lines = ['a', ' b', ' d']
>>> all(not x.startswith(' ') for x in lines)
False
>>> lines = ['a', 'b', 'd']
>>> all(not x.startswith(' ') for x in lines)
True

Also there's no need to load all lines in memory, simply iterate over the file object:

with open('filename') as f:
   res = all(not line.startswith(' ') for line in f)

Answer 2

Use the all built-in.

return all(not line.startswith(' ') for line in lines)

The all() function from the docs:

 all(iterable) -> bool Return True if bool(x) is True for all values x in the iterable. If the iterable is empty, return True. 

---

You could also use the any built-in in the same manner.

return not any(line.startswith(' ') for line in lines)

The any() function from the docs:

 any(iterable) -> bool Return True if bool(x) is True for any x in the iterable. If the iterable is empty, return False. 

Answer 3

with open('filename') as f:
    res = True
    for line in f:
        if line.startswith(' '):
            res = False
            break
return res