如何找到Python的hashlib的实现(见截图)?

Question

1 在hashlib.py中貌似找不到md5()这些东西
2 hashlib.py也没有import什么东西

Answer 1

hashlib里因为会有类似Crypto的数字计算，如果纯用python做的话，速度很慢，达不到要求，因此这个具体的实现是放在_hashlib.pyd，对于Python2.7, 路径位于C:\Python27\DLLs_hashlib.pyd，采用C实现的这个动态库里

import hashlib
print help(hashlib.md5)

import _hashlib
print help(_hashlib.openssl_md5)


# 生成的MD5值一样
S = "this is a demo for md5"
assert hashlib.md5(S).hexdigest() == _hashlib.openssl_md5(S).hexdigest()

加载过程为：

try:
    import _hashlib
    new = __hash_new
    __get_hash = __get_openssl_constructor
    algorithms_available = algorithms_available.union(
        _hashlib.openssl_md_meth_names)
except ImportError:
    new = __py_new
    __get_hash = __get_builtin_constructor

for __func_name in __always_supported:
    # try them all, some may not work due to the OpenSSL
    # version not supporting that algorithm.
    try:
        globals()[__func_name] = __get_hash(__func_name)
    except ValueError:
        import logging
        logging.exception('code for hash %s was not found.', __func_name)


try:
    # OpenSSL's PKCS5_PBKDF2_HMAC requires OpenSSL 1.0+ with HMAC and SHA
    from _hashlib import pbkdf2_hmac
except ImportError:
    import binascii
    import struct

    _trans_5C = b"".join(chr(x ^ 0x5C) for x in range(256))
    _trans_36 = b"".join(chr(x ^ 0x36) for x in range(256))

    def pbkdf2_hmac(hash_name, password, salt, iterations, dklen=None):
        """Password based key derivation function 2 (PKCS #5 v2.0)

        This Python implementations based on the hmac module about as fast
        as OpenSSL's PKCS5_PBKDF2_HMAC for short passwords and much faster
        for long passwords.
        """
        if not isinstance(hash_name, str):
            raise TypeError(hash_name)

        if not isinstance(password, (bytes, bytearray)):
            password = bytes(buffer(password))
        if not isinstance(salt, (bytes, bytearray)):
            salt = bytes(buffer(salt))

        # Fast inline HMAC implementation
        inner = new(hash_name)
        outer = new(hash_name)
        blocksize = getattr(inner, 'block_size', 64)
        if len(password) > blocksize:
            password = new(hash_name, password).digest()
        password = password + b'\x00' * (blocksize - len(password))
        inner.update(password.translate(_trans_36))
        outer.update(password.translate(_trans_5C))

        def prf(msg, inner=inner, outer=outer):
            # PBKDF2_HMAC uses the password as key. We can re-use the same
            # digest objects and just update copies to skip initialization.
            icpy = inner.copy()
            ocpy = outer.copy()
            icpy.update(msg)
            ocpy.update(icpy.digest())
            return ocpy.digest()

        if iterations < 1:
            raise ValueError(iterations)
        if dklen is None:
            dklen = outer.digest_size
        if dklen < 1:
            raise ValueError(dklen)

        hex_format_string = "%%0%ix" % (new(hash_name).digest_size * 2)

        dkey = b''
        loop = 1
        while len(dkey) < dklen:
            prev = prf(salt + struct.pack(b'>I', loop))
            rkey = int(binascii.hexlify(prev), 16)
            for i in xrange(iterations - 1):
                prev = prf(prev)
                rkey ^= int(binascii.hexlify(prev), 16)
            loop += 1
            dkey += binascii.unhexlify(hex_format_string % rkey)

        return dkey[:dklen]

# Cleanup locals()
del __always_supported, __func_name, __get_hash
del __py_new, __hash_new, __get_openssl_constructor