Merging two files in python - python-2.7

Question

In python 2.7.3, I try to merge two files in one.
I download a file over the Internet. The entire file size is exactly 3,197,743 bytes. I download it in two parts, one part is 3,000,000 bytes in size, the second part is 197,743 in size. Then, I want to merge the two files to reconstruct the entire file.
Here my code :
import requests
import shutil
URL = 'some_URL'
headers = {'user-agent': 'Agent'}
headers.update({'range': 'bytes=0-2999999'})
response = requests.get(URL, headers=headers)
file = open('some_file', 'wb')
file.write(response.content)
file.close()
headers2 = {'user-agent': 'Agent'}
headers2.update({'range': 'bytes=3000000-'})
response2 = requests.get(URL, headers=headers2)
file2 = open('some_file2', 'wb')
file2.write(response2.content)
file2.close()
source = open('some_file2','rb')
destination = open('some_file','ab')
shutil.copyfileobj(source,destination)
destination.close()
source.close()
At the end, I have one file ('some-file' in the example) which size is exactly 3,197,743 bytes but the file is corrupted. I tried this with a PDF file.
Where is the problem ?

Answer 1

I tried to solve your problem with different approaches and used diff tool to identify whether the program retrieves part files differently. I identified that there are no difference, thus I am not really sure what's wrong.
However, I propose following solution to resolve your usecase
import urllib2
URL = "http://traffic.org/general-reports/traffic_pub_gen19.pdf"
req = urllib2.urlopen(URL)
CHUNK = 3000000
with open("some_file.pdf", 'wb') as fp:
while True:
chunk = req.read(CHUNK)
if not chunk: break
fp.write(chunk)