How do I calculate the MD5 checksum of a file in Python

Question

I have written some code in Python that checks for an MD5 hash in a file and makes sure the hash matches that of the original  Here is what I have developed    Defines filename filename    quot file exe quot     Gets MD5 from file  def getmd5 filename       return m hexdigest    md5   dict    for fname in filename      md5 fname    getmd5 fname     If statement for alerting the user whether the checksum passed or failed  if md5      gt md5 will go here lt         print  quot MD5 Checksum passed  You may now close this window quot       input   quot press enter quot   else      print  quot MD5 Checksum failed  Incorrect MD5 in file  filename   Please download a new copy quot       input  quot press enter quot    exit  But whenever I run the code  I get the following error  Traceback  most recent call last   File  quot C  Users Username md5check py quot   line 13  in  lt module gt   md5 fname    getmd5 fname  File  quot C  Users Username md5check py  line 9  in getmd5   return m hexdigest   NameError  global name  m  is not defined  Is there anything I am missing in my code

User · Answer

You can calculate the checksum of a file by reading the binary data and using hashlib md5   hexdigest    A function to do this would look like the following  def File Checksum Dis dirname            if not os path exists dirname           print dirname  quot  directory is not existing quot             for fname in os listdir dirname           if not fname endswith                   fnaav   os path join dirname  fname               fd   open fnaav   rb                data   fd read                fd close                         print  quot - quot  70               print  quot File Name is   quot  fname                         print hashlib md5 data  hexdigest                print  quot - quot  70

User · Answer

In Python 3 8  you can do import hashlib  with open  quot your filename png quot    quot rb quot   as f      file hash   hashlib md5       while chunk    f read 8192           file hash update chunk   print file hash digest    print file hash hexdigest       to get a printable str instead of bytes  On Python 3 7 and below  with open  quot your filename png quot    quot rb quot   as f      file hash   hashlib md5       chunk   f read 8192      while chunk          file hash update chunk          chunk   f read 8192   print file hash hexdigest     This reads the file 8192  or 2      bytes at a time instead of all at once with f read   to use less memory   Consider using hashlib blake2b instead of md5  just replace md5 with blake2b in the above snippets   It s cryptographically secure and faster than MD5

User · Answer

In regards to your error and what s missing in your code  m is a name which is not defined for getmd5   function    No offence  I know you are a beginner  but your code is all over the place  Let s look at your issues one by one      First  you are not using hashlib md5 hexdigest   method correctly  Please refer explanation on hashlib functions in Python Doc Library  The correct way to return MD5 for provided string is to do something like this    gt  gt  gt  import hashlib  gt  gt  gt  hashlib md5  filename exe   hexdigest    2a53375ff139d9837e93a38a279d63e5    However  you have a bigger problem here  You are calculating MD5 on a file name string  where in reality MD5 is calculated based on file contents  You will need to basically read file contents and pipe it though MD5  My next example is not very efficient  but something like this    gt  gt  gt  import hashlib  gt  gt  gt  hashlib md5 open  filename exe   rb   read    hexdigest    d41d8cd98f00b204e9800998ecf8427e    As you can clearly see second MD5 hash is totally different from the first one  The reason for that is that we are pushing contents of the file through  not just file name    A simple solution could be something like that     Import hashlib library  md5 method is part of it  import hashlib    File to check file name    filename exe     Correct original md5 goes here original md5    5d41402abc4b2a76b9719d911017c592       Open close  read file and calculate MD5 on its contents  with open file name  as file to check        read contents of the file     data   file to check read             pipe contents of the file through     md5 returned   hashlib md5 data  hexdigest      Finally compare original MD5 with freshly calculated if original md5    md5 returned      print  MD5 verified   else      print  MD5 verification failed      Please look at the post Python  Generating a MD5 checksum of a file  It explains in detail a couple of ways how it can be achieved efficiently   Best of luck

[python] How do I calculate the MD5 checksum of a file in Python?

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