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COBOL Copybook parser in Python

This is a COBOL Copybook parser in Python featuring the following options:

  • Parse the Copybook into a usable format to use in Python
  • Clean up the Copybook by processing REDEFINES statements and remove unused definitions
  • Denormalize the Copybook
  • Write the cleaned Copybook in COBOL
  • Strip prefixes of field names and ensure that the Copybook only contains unique names
  • Can be used from the command-line or included in own Python projects

Because I couldn't find a COBOL Copybook parser that fitted all my needs I wrote my own. It doesn't support all functions found in the Copybook, just the ones that I met on my path: REDEFINES, INDEXED BY, OCCURS.

On a day to day basis I use it so that Informatica PowerCenter creates only 1 table of my COBOL data instead multiple.

The code uses the pic parser code from pyCOBOL.

This code is licensed under GPLv3.

Example output

Below is an example Copybook file before and after being processed.

Before:

00000 * Example COBOL Copybook file                                     AAAAAAAA
00000  01  PAULUS-EXAMPLE-GROUP.                                        AAAAAAAA
00000       05  PAULUS-ANOTHER-GROUP OCCURS 0003 TIMES.                 AAAAAAAA
00000           10  PAULUS-FIELD-1 PIC X(3).                            AAAAAAAA
00000           10  PAULUS-FIELD-2 REDEFINES PAULUS-FIELD-1 PIC 9(3).   AAAAAAAA
00000           10  PAULUS-FIELD-3 OCCURS 0002 TIMES                    AAAAAAAA
00000                           PIC S9(3)V99.                           AAAAAAAA
00000       05  PAULUS-THIS-IS-ANOTHER-GROUP.                           AAAAAAAA
00000           10  PAULUS-YES PIC X(5).                                AAAAAAAA

After:

         01  EXAMPLE-GROUP.                                                     
           05  FIELD-2-1 PIC 9(3).                                              
           05  FIELD-3-1-1 PIC S9(3)V99.                                        
           05  FIELD-3-1-2 PIC S9(3)V99.                                        
           05  FIELD-2-2 PIC 9(3).                                              
           05  FIELD-3-2-1 PIC S9(3)V99.                                        
           05  FIELD-3-2-2 PIC S9(3)V99.                                        
           05  FIELD-2-3 PIC 9(3).                                              
           05  FIELD-3-3-1 PIC S9(3)V99.                                        
           05  FIELD-3-3-2 PIC S9(3)V99.                                        
           05  THIS-IS-ANOTHER-GROUP.                                           
             10  YES PIC X(5).

How to use

You can use it in two ways: inside your own python code or as a stand-alone command-line utility.

Command-line

Do a git clone from the repository and inside your brand new python-cobol folder run:

python cobol.py example.cbl

This will process the redefines, denormalize the file, strip the prefixes and ensure all names are unique.

The utility allows for some command-line switches to disable some processing steps.

$ python cobol.py --help
usage: cobol.py [-h] [--skip-all-processing] [--skip-unique-names]
                      [--skip-denormalize] [--skip-strip-prefix]
                      filename

Parse COBOL Copybooks

positional arguments:
  filename              The filename of the copybook.

optional arguments:
  -h, --help            show this help message and exit
  --skip-all-processing
                        Skips unique names, denormalization and .
  --skip-unique-names   Skips making all names unique.
  --skip-denormalize    Skips denormalizing the COBOL.
  --skip-strip-prefix   Skips stripping the prefix from the names.

From within your Python code

The parser can also be called from your Python code. All you need is a list of lines in COBOL Copybook format. See example.py how one would do it:

import cobol

with open("example.cbl",'r') as f:
    for row in cobol.process_cobol(f.readlines()):
    	print row['name']

It is also possible to call one of the more specialized functions within cobol.py:

  • clean_cobol(lines)

    Cleans the COBOL by converting the cobol informaton to single lines

  • parse_cobol(lines)

    Parses a list of COBOL field definitions into a list of dictionaries containing the parsed information.

  • denormalize_cobol(lines)

    Denormalizes parsed COBOL lines

  • clean_names(lines, ensure_unique_names=False, strip_prefix=False, make_database_safe=False)

    Cleans names of the fields in a list of parsed COBOL lines. Options to strip prefixes, enforce unique names and make the names database safe by converting dashes (-) to underscores (_)

  • print_cobol(lines)

    Prints parsed COBOL lines in the Copybook format