以下是我对Piotr Czapla方法的看法:

def md5sum(filename):
    md5 = hashlib.md5()
    with open(filename, 'rb') as f:
        for chunk in iter(lambda: f.read(128 * md5.block_size), b''):
            md5.update(chunk)
    return md5.hexdigest()

Python < 3.7

import hashlib

def checksum(filename, hash_factory=hashlib.md5, chunk_num_blocks=128):
    h = hash_factory()
    with open(filename,'rb') as f: 
        for chunk in iter(lambda: f.read(chunk_num_blocks*h.block_size), b''): 
            h.update(chunk)
    return h.digest()

Python 3.8及以上版本

import hashlib

def checksum(filename, hash_factory=hashlib.md5, chunk_num_blocks=128):
    h = hash_factory()
    with open(filename,'rb') as f: 
        while chunk := f.read(chunk_num_blocks*h.block_size): 
            h.update(chunk)
    return h.digest()

最初的发布

如果你想要一个更Pythonic (no while True)的方式读取文件，检查下面的代码:

import hashlib

def checksum_md5(filename):
    md5 = hashlib.md5()
    with open(filename,'rb') as f: 
        for chunk in iter(lambda: f.read(8192), b''): 
            md5.update(chunk)
    return md5.digest()

请注意，iter()函数需要一个空字节字符串，以便返回的迭代器在EOF处停止，因为read()返回b "(不仅仅是")。

Bastien Semene的代码的混合，考虑了Hawkwing关于通用哈希函数的评论…

def hash_for_file(path, algorithm=hashlib.algorithms[0], block_size=256*128, human_readable=True):
    """
    Block size directly depends on the block size of your filesystem
    to avoid performances issues
    Here I have blocks of 4096 octets (Default NTFS)

    Linux Ext4 block size
    sudo tune2fs -l /dev/sda5 | grep -i 'block size'
    > Block size:               4096

    Input:
        path: a path
        algorithm: an algorithm in hashlib.algorithms
                   ATM: ('md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512')
        block_size: a multiple of 128 corresponding to the block size of your filesystem
        human_readable: switch between digest() or hexdigest() output, default hexdigest()
    Output:
        hash
    """
    if algorithm not in hashlib.algorithms:
        raise NameError('The algorithm "{algorithm}" you specified is '
                        'not a member of "hashlib.algorithms"'.format(algorithm=algorithm))

    hash_algo = hashlib.new(algorithm)  # According to hashlib documentation using new()
                                        # will be slower then calling using named
                                        # constructors, ex.: hashlib.md5()
    with open(path, 'rb') as f:
        for chunk in iter(lambda: f.read(block_size), b''):
             hash_algo.update(chunk)
    if human_readable:
        file_hash = hash_algo.hexdigest()
    else:
        file_hash = hash_algo.digest()
    return file_hash

你需要以合适大小的块读取文件:

def md5_for_file(f, block_size=2**20):
    md5 = hashlib.md5()
    while True:
        data = f.read(block_size)
        if not data:
            break
        md5.update(data)
    return md5.digest()

注意:确保你用'rb'打开你的文件-否则你会得到错误的结果。

所以要在一种方法中完成所有的事情-使用如下的方法:

def generate_file_md5(rootdir, filename, blocksize=2**20):
    m = hashlib.md5()
    with open( os.path.join(rootdir, filename) , "rb" ) as f:
        while True:
            buf = f.read(blocksize)
            if not buf:
                break
            m.update( buf )
    return m.hexdigest()

上面的更新是基于Frerich Raabe提供的评论——我测试了一下，发现在我的Python 2.7.2 Windows安装上是正确的

我用jacksum工具反复核对了结果。

jacksum -a md5 <filename>

以下是我对Piotr Czapla方法的看法:

def md5sum(filename):
    md5 = hashlib.md5()
    with open(filename, 'rb') as f:
        for chunk in iter(lambda: f.read(128 * md5.block_size), b''):
            md5.update(chunk)
    return md5.hexdigest()

将文件分解为8192字节的块(或其他128字节的倍数)，并使用update()将它们连续地馈送给MD5。

这利用了MD5有128字节摘要块的事实(8192是128×64)。由于不是将整个文件读入内存，因此使用的内存不会超过8192个字节。

在Python 3.8+中你可以这样做

import hashlib
with open("your_filename.txt", "rb") 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