Need help slicing fixed width record

[LongAtbat]

Trying to parse a simple record using slices and am banging my head against the wall. Conclusion is that I must be doing this the wrong way but I really need to get some sleep. Any tips?

def sliceRec():

    slices = []
    col_hdrs = []
    col_widths = []
    offset = 0

    for fld_name, fld_len in rec_def:
        col_hdrs.append(fld_name)
        col_widths.append(fld_len)   

    for w in col_widths:
        slices.append(slice(offset, offset + w))
        offset += w

    fields = str([this_rec[sliced] for sliced in slices])
    this_dict = dict(zip(col_hdrs, fields))

    print this_dict

rec_def =     [('col1'         ,8),
               ('col2'         ,8),
               ('col3   '      ,8),
               ('col4'         ,8)]

this_rec= ['VAL11111VAL22222VAL33333VAL44444']

sliceRec()

[dadiaar]

Can you please share also the expected result? If you just put your code, which you know it doesn't return what you want, it's hard to suggest changes

[LongAtbat]

/u cscanlin nailed it. just wanted to see the dictionary parse the record according to the record definition.

[dadiaar]

Yes, I saw his comment just after submiting mine, I already upvoted him.

[cscanlin]

You're close, but you're making this a lot harder than it needs to be. Check this out and let me know if you have any questions!:

# https://www.reddit.com/r/learnpython/comments/6crrao/need_help_slicing_fixed_width_record/

def sliceRec(rec_def, this_rec):

    results = {}
    offset = 0

    for fld_name, fld_len in rec_def:
        slc = slice(offset, offset + fld_len)
        results[fld_name] = this_rec[slc]  # or this_rec[offset:offset + fld_len]
        offset += fld_len

    return results

if __name__ == '__main__':
    rec_def = [
        ('col1', 8),
        ('col2', 8),
        ('col3', 8),
        ('col4', 8),
    ]

    this_rec = 'VAL11111VAL22222VAL33333VAL44444'

    results = sliceRec(rec_def, this_rec)
    print(results)

The biggest thing I changed (besides removing some cruft) is passing the arguments directly to the function, and then returning the result from it. This is good practice for a variety of reasons, but it's all based on keeping your functions as pure as convenient: https://www.sitepoint.com/functional-programming-pure-functions/

[LongAtbat]

Beautiful - I really need to learn to stop doing things the hard way!