Get size of a file before downloading in Python

Question

I'm downloading an entire directory from a web server. It works OK, but I can't figure how to get the file size before download to compare if it was updated on the server or not. Can this be done as if I was downloading the file from a FTP server?

import urllib
import re

url = "http://www.someurl.com"

# Download the page locally
f = urllib.urlopen(url)
html = f.read()
f.close()

f = open ("temp.htm", "w")
f.write (html)
f.close()

# List only the .TXT / .ZIP files
fnames = re.findall('^.*<a href="(\w+(?:\.txt|.zip)?)".*$', html, re.MULTILINE)

for fname in fnames:
    print fname, "..."

    f = urllib.urlopen(url + "/" + fname)

    #### Here I want to check the filesize to download or not #### 
    file = f.read()
    f.close()

    f = open (fname, "w")
    f.write (file)
    f.close()

---

@Jon: thank for your quick answer. It works, but the filesize on the web server is slightly less than the filesize of the downloaded file.

Examples:

Local Size  Server Size
 2.223.533  2.115.516
   664.603    662.121

It has anything to do with the CR/LF conversion?

Answer 1

I have reproduced what you are seeing:

import urllib, os
link = "http://python.org"
print "opening url:", link
site = urllib.urlopen(link)
meta = site.info()
print "Content-Length:", meta.getheaders("Content-Length")[0]

f = open("out.txt", "r")
print "File on disk:",len(f.read())
f.close()


f = open("out.txt", "w")
f.write(site.read())
site.close()
f.close()

f = open("out.txt", "r")
print "File on disk after download:",len(f.read())
f.close()

print "os.stat().st_size returns:", os.stat("out.txt").st_size

Outputs this:

opening url: http://python.org
Content-Length: 16535
File on disk: 16535
File on disk after download: 16535
os.stat().st_size returns: 16861

What am I doing wrong here? Is os.stat().st_size not returning the correct size?

---

Edit: OK, I figured out what the problem was:

import urllib, os
link = "http://python.org"
print "opening url:", link
site = urllib.urlopen(link)
meta = site.info()
print "Content-Length:", meta.getheaders("Content-Length")[0]

f = open("out.txt", "rb")
print "File on disk:",len(f.read())
f.close()


f = open("out.txt", "wb")
f.write(site.read())
site.close()
f.close()

f = open("out.txt", "rb")
print "File on disk after download:",len(f.read())
f.close()

print "os.stat().st_size returns:", os.stat("out.txt").st_size

this outputs:

$ python test.py
opening url: http://python.org
Content-Length: 16535
File on disk: 16535
File on disk after download: 16535
os.stat().st_size returns: 16535

Make sure you are opening both files for binary read/write.

// open for binary write
open(filename, "wb")
// open for binary read
open(filename, "rb")

Answer 2

Using the returned-urllib-object method info(), you can get various information on the retrived document. Example of grabbing the current Google logo:

>>> import urllib
>>> d = urllib.urlopen("http://www.google.co.uk/logos/olympics08_opening.gif")
>>> print d.info()

Content-Type: image/gif
Last-Modified: Thu, 07 Aug 2008 16:20:19 GMT  
Expires: Sun, 17 Jan 2038 19:14:07 GMT 
Cache-Control: public 
Date: Fri, 08 Aug 2008 13:40:41 GMT 
Server: gws 
Content-Length: 20172 
Connection: Close

It's a dict, so to get the size of the file, you do urllibobject.info()['Content-Length']

print f.info()['Content-Length']

And to get the size of the local file (for comparison), you can use the os.stat() command:

os.stat("/the/local/file.zip").st_size

Answer 3

The size of the file is sent as the Content-Length header. Here is how to get it with urllib:

>>> site = urllib.urlopen("http://python.org")
>>> meta = site.info()
>>> print meta.getheaders("Content-Length")
['16535']
>>>

Answer 4

Also if the server you are connecting to supports it, look at Etags and the If-Modified-Since and If-None-Match headers.

Using these will take advantage of the webserver's caching rules and will return a 304 Not Modified status code if the content hasn't changed.

Answer 5

In Python3:

>>> import urllib.request
>>> site = urllib.request.urlopen("http://python.org")
>>> print("FileSize: ", site.length)

Answer 6

For a python3 (tested on 3.5) approach I'd recommend:

with urlopen(file_url) as in_file, open(local_file_address, 'wb') as out_file:
    print(in_file.getheader('Content-Length'))
    out_file.write(response.read())

Answer 7

A requests-based solution using HEAD instead of GET (also prints HTTP headers):

#!/usr/bin/python
# display size of a remote file without downloading

from __future__ import print_function
import sys
import requests

# number of bytes in a megabyte
MBFACTOR = float(1 << 20)

response = requests.head(sys.argv[1], allow_redirects=True)

print("\n".join([('{:<40}: {}'.format(k, v)) for k, v in response.headers.items()]))
size = response.headers.get('content-length', 0)
print('{:<40}: {:.2f} MB'.format('FILE SIZE', int(size) / MBFACTOR))

Usage

$ python filesize-remote-url.py https://httpbin.org/image/jpeg
...
Content-Length                          : 35588
FILE SIZE (MB)                          : 0.03 MB