Iterate through two files to create a new file that has fields from second file appended to fields of first file

Question

I am new to Python. I attempted to use logic from answers in @mgilson, @endolith, and @zackbloom zack's example

1. I am getting a bunch of blank columns placed in front of the first field of the primary record.
2. My out_file is empty (more than likely because of the columns from the two files cannot match up.

How can I fix this? The end result should look like the following:

('PUDO_id','Load_id','carrier_id','PUDO_from_company','PUDOItem_id';'PUDO_id';'PUDOItem_make')              
('1','1','14','FMH MATERIAL HANDLING SOLUTIONS','1','1','CROWN','TR3520 / TWR3520','TUGGERS')
('2','2','7','WIESE USA','2','2','CAT','NDC100','3','2','CAT','NDC100','4','2',' 2 BATTERIES')

Note: In the output of the 3rd row, it appended 3 rows from the sub file to the array, while the first 2 rows only appended 1 row from the sub file. This is determined by the value in pri[0] and sub[1] comparing TRUE.

Here is my code based on @Zack Bloom:

def build_set(filename):
    # A set stores a collection of unique items.  Both adding items and searching for them
    # are quick, so it's perfect for this application.
    found = set()

    with open(filename) as f:
        for line in f:
                # Tuples, unlike lists, cannot be changed, which is a requirement for anything
                # being stored in a set.
                line = line.replace('"','')
                line = line.replace("'","")
                line = line.replace('\n','')
                found.add(tuple(sorted(line.split(';'))))
    return found

set_primary_records = build_set('C:\\temp\\oz\\loads_pudo.csv')
set_sub_records     = build_set('C:\\temp\\oz\\pudo_items.csv')
record                  = []

with open('C:\\temp\\oz\\loads_pudo_out.csv', 'w') as out_file:
   # Using with to open files ensures that they are properly closed, even if the code
   # raises an exception.

    for pri in set_primary_records :
        for sub in set_sub_records :
            #out_file.write(" ".join(res) + "\n")
            if sub[1] == pri [0] :
                record = pri.extend(sub)
            out_file.write(record + '\n')

Sample source data (primary records):

PUDO_id;"Load_id";"carrier_id";"PUDO_from_company"              
1;"1";"14";"FMH MATERIAL HANDLING SOLUTIONS"                
2;"2";"7";"WIESE USA"

Sample source data (sub records):

PUDOItem_id;"PUDO_id";"PUDOItem_make"
1;"1";"CROWN";"TR3520 / TWR3520";"TUGGERS"
2;"2";" CAT";"NDC100"
3;"2";"CAT";"NDC100"
4;"2";" 2 BATTERIES"
5;"11";"MIDLAND"

Answer 1

The extend attribute is not available for tuples which is what build_set is creating. Tuples are immutable but they can be concatenated or sliced with normal python string functions.

For example:

with open('C:\\temp\\oz\\loads_pudo_out.csv', 'w') as out_file:
    for pri in set_primary_records :
        for sub in set_sub_records :
            if sub[1] == pri[0] :
                record = pri + sub
                out_file.write(str(record)[1:-1] + '\n')

This is the same code as above, just modified to allow for tuple concatenation. In the write line we convert record to a string and strip the start and end brackets, before appending '\n'. Maybe there are better / prettier ways to do this, but I'm new to Python too.

Edit: To get the output you are expecting, a few changes are required:

# On this line, remove the sort() as we do not wish to change tuple item order..
found.add(tuple(line.split(';')))

...

with open('C:\\temp\\loads_out.csv', 'w') as out_file:
    for pri in set_primary_records:
        record = pri                        # record tuple is set in main loop
        for sub in set_sub_records:
            if sub[1] == pri[0]:
                record += sub               # for each match, sub appended to record
        out_file.write(str(record) + '\n')  # removed stripping of brackets