On PEP 312: simple implicit lambda

[Manuel M. Garcia]

On Sun, 16 Feb 2003 16:47:11 +0200, Christos "TZOTZIOY" Georgiou
<DLNXPEGFQVEB at spammotel.com> wrote:
(edit)
>Take for example:
>
>data = file_object.read(4096)
>while data:
>    # process here
>     data = file_object.read(4096)
(edit)
><read_more_data>:
>    data = file_object.read(4096)
>while data:
>	# process here
>    <read_more_data>

The usual idiom used in this case is:

    while 1:
        data = file_object.read(4096)
        if not data: break
        # process here

I agree it is not perfect.  I never prefer an infinite loop, and I
always try my best to put the loop termination condition as part of
the 'while' statement.

Here is another Python trick inside of a little test program:

# ###################################### #
# tzotzioy_loop01.py

import sys

def store_data(f):
    """adds a .data attribute to a function to
    store the last result"""
    class _:
        def __call__(self):
            self.data = f()
            return self.data
    return _()

file_object = file('tzotzioy_loop01.py')
_readline = store_data( file_object.readline )
i = 0
while _readline():
    i += 1
    sys.stdout.write('%03i %s' % (i, _readline.data))

# ###################################### #

Using the trick of a temporary class, you have a good place to store
'.data' for later use if the function call is sucessful.

Manuel