David542 David542 - 5 months ago 14
Python Question

Getting percentage complete of an md5 checksum

I am currently getting an md5 checksum as follows:

>>> import hashlib
>>> f = open(file)
>>> m = hashlib.md5()
>>> m.update(f.read())
>>> checksum = m.hedxigest()


I need to return the checksum of a large video file, that will take several minutes to generate. How would I implement a percentage counter, such that it prints the percentage complete for each percentage while it is running. Something like:

>>> checksum = m.hedxigest()
1% done...
2% done...
etc.

Answer

You can call the update() method repeatedly and feed the file in chunks to it. Thus, you can show the progress yourself.

import hashlib
import os

def digest_with_progress(filename, chunk_size):
    read_size = 0
    last_percent_done = 0
    digest = hashlib.md5()
    total_size = os.path.getsize(filename)

    data = True
    f = open(filename)
    while data:
        # Read and update digest.
        data = f.read(chunk_size)
        read_size += len(data)
        digest.update(data)

        # Calculate progress.
        percent_done = 100 * read_size / total_size
        if percent_done > last_percent_done:
            print '%d%% done' % percent_done
            last_percent_done = percent_done
    f.close()
    return digest.hexdigest()

When I try print digest_with_progress('/bin/bash', 1024) this is what I get:

1% done
2% done
3% done
4% done
5% done
6% done
7% done
8% done
9% done
10% done
11% done
12% done
13% done
14% done
15% done
16% done
17% done
18% done
19% done
20% done
21% done
22% done
23% done
24% done
25% done
26% done
27% done
28% done
29% done
30% done
31% done
32% done
33% done
34% done
35% done
36% done
37% done
38% done
39% done
40% done
41% done
42% done
43% done
44% done
45% done
46% done
47% done
48% done
49% done
50% done
51% done
52% done
53% done
54% done
55% done
56% done
57% done
58% done
59% done
60% done
61% done
62% done
63% done
64% done
65% done
66% done
67% done
68% done
69% done
70% done
71% done
72% done
73% done
74% done
75% done
76% done
77% done
78% done
79% done
80% done
81% done
82% done
83% done
84% done
85% done
86% done
87% done
88% done
89% done
90% done
91% done
92% done
93% done
94% done
95% done
96% done
97% done
98% done
99% done
100% done
b114ecaab65bc5b02f5a129bd29d1864

Here are the actual details of this file.

$ ls -l /bin/bash; md5sum /bin/bash
-rwxr-xr-x 1 root root 971384 Nov 30 16:31 /bin/bash
b114ecaab65bc5b02f5a129bd29d1864  /bin/bash

Note that, you would not get the expected output if you make chunk_size too large. For example if we read in 100 KB chunks instead of 1 KB chunks for /bin/bash, this is what you see.

10% done
21% done
31% done
42% done
52% done
63% done
73% done
84% done
94% done
100% done
b114ecaab65bc5b02f5a129bd29d1864

The limitation of this approach is that we calculate the progress only after we have read a chunk into the digest. So, if the chunk size is too large, the percentage-difference in progress would be more than 1% every time you read a chunk and update the digest. A bigger chunk size would get the job done a bit quicker. So, you might want to relax the condition of printing percentage complete for each percentage in favour of efficiency.

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