Simple script that allows you to merge PDF files. You can also specify which pages to consider when merging.

pdf_merge.py

import argparse
import re
from pathlib import Path
from PyPDF2 import PdfMerger
from PyPDF2.errors import PyPdfError


def parse_pages(pages_list, files):
    # no ranges => select all pages
    # "None" means "all pages" in pypdf2
    if not pages_list:
        return [[None]] * len(files)

    r = re.compile(r'^(\(((?:(-?\d+ )?(-?\d+,-?\d+ )?(all )?)*)((-?\d+)|(-?\d+,-?\d+)|all)\))|all$')

    # will contain lists of ranges
    # where each list is associated with a file
    # e.g. [ [(0, 1), (2, 4)], [(1, 3)] ]
    parsed_pages = []

    for file, pages in zip(files, pages_list):
        if not r.match(pages):
            print(f'Syntax error: \"{pages}\".')
            return None

        # will contain parsed ranges for the current file
        # e.g. [ (0, 1), (2, 4) ]
        file_pages = []

        for p in pages.replace('(', '').replace(')', '').split(' '):
            if p == 'all':
                file_pages.append(None)
                continue

            # we can either have a single page number (x) or a range (x-y)
            try:
                file_pages.append((int(p), int(p) + 1))
            except ValueError:
                to_add = tuple(int(n) for n in p.split(','))

                if to_add[0] >= to_add[1]:
                    print(f'Start page is greater than or equal to final page in \"{p}\" for file \"{file}\".')
                    return None

                file_pages.append(to_add)

        parsed_pages.append(file_pages)

    return parsed_pages


def parse_arguments():
    parser = argparse.ArgumentParser(description='Simple PDF merger', usage='pdf_merge.py [-h] [-p [PAGES_LIST ...]] '
                                                                            '[-o OUTFILE] file1 [other_files ...]')
    parser.add_argument('files', nargs='+', help='List of files to merge\n'
                                                 'You can specify a single file '
                                                 'if you only want to extract certain pages')
    parser.add_argument('-p', '--pages-list', nargs='*', help='Pages to consider when merging:\n'
                                                              '\"(0,2)\"   => first two pages\n'
                                                              '\"(0 2,5)\" => first page + pages from third to fifth\n'
                                                              '\"(-1)\"    => last page\n'
                                                              '\"all\"     => the whole document')
    parser.add_argument('-o', '--outfile', default='merged.pdf', help='Name of output file')

    parser.formatter_class = argparse.RawTextHelpFormatter

    args = parser.parse_args()

    files, pages_list, outfile = args.files, args.pages_list, args.outfile

    if pages_list and len(pages_list) > len(files):
        print(f'Number of ranges is greater than number of files. '
              f'Last {len(pages_list)-len(files)} range(s) will be ignored.')
        pages_list = parse_pages(pages_list[:len(files)-len(pages_list)], files)
    elif pages_list and len(pages_list) < len(files):
        print(f'Number of ranges is less than number of files. '
              f'Last {len(files)-len(pages_list)} file(s) will be treated in full.')
        pages_list = parse_pages(pages_list, files)
        pages_list and pages_list.extend([[None]] * (len(files)-len(pages_list)))
    else:
        pages_list = parse_pages(pages_list, files)

    if not re.match(r'^.*\.pdf$', outfile):
        outfile = outfile + '.pdf'

    if outfile in files:
        print(f'Output file name ({outfile}) is the same as one of the specified files.')
        outfile = None

    return files, pages_list, outfile


def main():
    files, pages_list, outfile = parse_arguments()

    if not pages_list or not outfile:
        return

    with PdfMerger() as merger:
        for file, pages in zip(files, pages_list):
            if not file or not Path(file).is_file():
                print(f'Invalid path: \"{file}\".')
                return

            for p in pages:
                try:
                    merger.append(file, pages=p)
                except PyPdfError:
                    print(f'Invalid file: \"{file}\".')
                    return
                except IndexError:
                    print(f'Page range \"{p}\" out of bounds for file \"{file}\".')
                    return

        try:
            merger.write(outfile)
            print(f'Files successfully merged into \"{outfile}\".')
        except PyPdfError:
            print('Couldn\'t merge files.')
        except PermissionError:
            print(f'Couldn\'t write to output file: permission denied.')
        except OSError:
            print(f'Invalid output file name: \"{outfile}\".')


if __name__ == '__main__':
    main()