Resume HTTP download proof of concept (POC) / minimum viable product (MVP). Let unstable internet be no problem working with pip on the road, please.

file_downloader.py

"""Download with automatic resume.
2018-06-28 v1.0 by Cees Timmerman
2018-07-09 v1.1 Added If-Unmodified-Since header for consistency."""
import os, shutil, sys, time
import requests  # python -m pip install requests

def download_file(url, local_filename=None):
	if not local_filename:
		local_filename = url.split('/')[-1]
	
	resume_byte_pos = 0
	try:
		resume_byte_pos = os.path.getsize(local_filename)
		mtime = os.path.getmtime(local_filename)
	except: pass

	headers = {}
	if resume_byte_pos:
		headers.update(Range='bytes=%d-' % resume_byte_pos)
		#headers.update({"If-Range": time.strftime('%a, %d %b %Y %H:%M:%S GMT', time.gmtime(mtime))})  # Never matches?
		headers.update({"If-Unmodified-Since": time.strftime('%a, %d %b %Y %H:%M:%S GMT', time.gmtime(mtime))})
		print("Requesting", headers)

	with requests.get(
			url,
			headers=headers,
			stream=True,  # Save RAM.
			verify=False,
			allow_redirects=True
	) as r:
		print("Received", r.headers)
		if r.status_code == 206:
			print('Resuming download')
			mode = 'ab'
		elif r.status_code == 200:
			print('(Re)starting download')
			mode = 'wb'
		else:
			raise Exception("Unexpected HTTP status in", r)
		with open(local_filename, mode) as f:
			shutil.copyfileobj(r.raw, f)

if __name__ == "__main__":
	'''
	open('test_server_data', 'wb').write(b'1234567890'*20)
	sent = open('test_server_data', 'rb').read()
	print("Wrote:")
	print(sent[:50], sent[-50:])
	download_file('http://localhost:8000/test_server_data', 'downloaded_data')  # python -m http.server
	print("Received:")
	received = open('downloaded_data', 'rb').read()
	print(received[:50], received[-50:])
	'''

	download_file('https://files.pythonhosted.org/packages/5d/85/d174a50e0d6b60aa9113f6a32afb31f25345bec8584992af486235373252/PyQt5-5.11.2-5.11.1-cp35.cp36.cp37.cp38-none-win_amd64.whl')
	"""
	Received {'x-amz-id-2': '62GbFKUpcBCcdmNASaQOnkDKP8pqpkuQyZlJZ7E/E5XKRWH2UYHo3GoLgdH7mjoFGcTKlkgGL1k=', 'x-amz-request-id': 'D197A6E08A790C75', 'Last-Modified': 'Mon, 02 Jul 2018 10:08:26 GMT', 'ETag': '"1423c667f7a669b86fb726047c6622bb-12"', 'x-amz-version-id': 'tGHd1dEMyUmr0S68pWjuVsaUmSE.Cf1P', 'Content-Type': 'binary/octet-stream', 'Server': 'AmazonS3', 'Cache-Control': 'max-age=365000000, immutable, public', 'Accept-Ranges': 'bytes, bytes', 'Age': '617529', 'Content-Length': '93349595', 'Date': 'Mon, 09 Jul 2018 13:41:01 GMT', 'Connection': 'keep-alive', 'X-Served-By': 'cache-sea1036-SEA, cache-ams4431-AMS', 'X-Cache': 'HIT, HIT', 'X-Cache-Hits': '0, 0', 'X-Timer': 'S1531143662.786994,VS0,VE1', 'Strict-Transport-Security': 'max-age=31536000; includeSubDomains; preload', 'X-Frame-Options': 'deny', 'X-XSS-Protection': '1; mode=block', 'X-Content-Type-Options': 'nosniff', 'X-Permitted-Cross-Domain-Policies': 'none', 'X-Robots-Header': 'noindex'}

	Requesting {'Range': 'bytes=58966016-'}
	Received {'x-amz-id-2': '62GbFKUpcBCcdmNASaQOnkDKP8pqpkuQyZlJZ7E/E5XKRWH2UYHo3GoLgdH7mjoFGcTKlkgGL1k=', 'x-amz-request-id': 'D197A6E08A790C75', 'Last-Modified': 'Mon, 02 Jul 2018 10:08:26 GMT', 'ETag': '"1423c667f7a669b86fb726047c6622bb-12"', 'x-amz-version-id': 'tGHd1dEMyUmr0S68pWjuVsaUmSE.Cf1P', 'Content-Type': 'binary/octet-stream', 'Server': 'AmazonS3', 'Cache-Control': 'max-age=365000000, immutable, public', 'Accept-Ranges': 'bytes, bytes', 'Age': '617810', 'Content-Range': 'bytes 58966016-93349594/93349595', 'Content-Length': '34383579', 'Date': 'Mon, 09 Jul 2018 13:45:43 GMT', 'Connection': 'keep-alive', 'X-Served-By': 'cache-sea1036-SEA, cache-ams4448-AMS', 'X-Cache': 'HIT, HIT', 'X-Cache-Hits': '0, 0', 'X-Timer': 'S1531143943.365115,VS0,VE1', 'Strict-Transport-Security': 'max-age=31536000; includeSubDomains; preload', 'X-Frame-Options': 'deny', 'X-XSS-Protection': '1; mode=block', 'X-Content-Type-Options': 'nosniff', 'X-Permitted-Cross-Domain-Policies': 'none', 'X-Robots-Header': 'noindex'}
	Resuming download
	"""
	

Because even Dutch mobile internet sucks.

To add a progress bar, replace the shutil.copyfileobj call with a read/write/report loop: https://stackoverflow.com/a/9740603/819417