file_copy + progress + hash generation + check

#!/usr/bin/env python3
"""
Program to copy a file from source to destination.
During the copy operation the hash value is calculated.
A progress bar is also supported.

If tqdm is not installed, it will install via
pip as a user site-package.
"""

import hashlib
import sys
import mmap
from argparse import ArgumentParser
from argparse import ArgumentDefaultsHelpFormatter as HelpFormatter
from pathlib import Path
from subprocess import call


def chunker(file_size, chunk_size):
    pos = 0
    while pos < file_size:
        next_pos = min(pos + chunk_size, file_size)
        yield slice(pos, next_pos)
        pos += chunk_size


def copy(src, dst, buffer_size, hash_algo, progress=False, check=False):
    file_size = src.stat().st_size
    if progress:
        progress_bar = tqdm(
            total=file_size,
            desc=f'Copy {src.name} > {dst.name}',
            unit="B", unit_scale=True,
            unit_divisor=1024,
            )
    hasher = hashlib.new(hash_algo)
    with src.open('rb') as src_fd:
        mm_src = mmap.mmap(src_fd.fileno(), 0, access=mmap.ACCESS_READ)
        with dst.open('r+b') as dst_fd:
            for data_slice in chunker(file_size, buffer_size):
                dst_fd.write(mm_src[data_slice])
                hasher.update(mm_src[data_slice])
                if progress:
                    progress_bar.update(data_slice.stop - data_slice.start)
            progress_bar.close()
            if check:
                dst_fd.seek(0)
                dst_hasher = hashlib.new(hash_algo)
                if progress:
                    progress_bar = tqdm(
                        total=file_size,
                        desc=f'Hashing {dst.name}',
                        unit="B", unit_scale=True,
                        unit_divisor=1024,
                    )
                while True:
                    chunk = dst_fd.read(buffer_size)
                    if not chunk:
                        break
                    if progress:
                        progress_bar.update(len(chunk))
                    dst_hasher.update(chunk)
                if progress:
                    progress_bar.close()
                check_result = True
                if dst_hasher.digest() == hasher.digest():
                    print('Written file is ok', file=sys.stderr)
                else:
                    print('Written file is different', file=sys.stderr)
                    check_result = False
    return hasher.hexdigest(), check_result


if __name__ == '__main__':
    hashes = hashlib.algorithms_available
    parser = ArgumentParser(description=__doc__, formatter_class=HelpFormatter)
    parser.add_argument('src', type=Path, help='Source file to copy')
    parser.add_argument('dst', type=Path, help='Destination file')
    parser.add_argument('hash', choices=hashes, help='Hash algorithm')
    parser.add_argument('--buffer', type=int, default=64 * 1024, help='Buffer size in bytes')
    parser.add_argument('--overwrite', action='store_true', help='Allow overwriting of destination file')
    parser.add_argument('--progress', action='store_true', help='Show a progress bar')
    parser.add_argument('--check', action='store_true', help='Read the destination file again and calculate the hash value')
    args = parser.parse_args()
    if not args.src.exists():
        print(f'Source file {args.src.name} does not exist.', file=sys.stderr)
        sys.exit(2)
    if not args.overwrite and args.dst.exists():
        print(f'Destination file {args.dst.name} exists.', file=sys.stderr)
        sys.exit(3)
    if args.progress:
        try:
            from tqdm import tqdm
        except ImportError:
            print('Python-Module tqdm is not installed, installing it now.', file=sys.stderr)
            call([sys.executable, '-m', 'pip', 'install', 'tqdm', '--user'])
            try:
                from tqdm import tqdm
            except ImportError:
                args.progress = False
            else:
                args.progress = True
        else:
            args.progress = True
    hex_digest, check_result = copy(args.src, args.dst, args.buffer, args.hash, args.progress, args.check)
    args.dst.with_suffix('.' + args.hash).write_text(f'{hex_digest}  {args.dst.name}\n')
    if not check_result:
        sys.exit(10)