hashlib中.digest()方法的作用是什么？为何要使用它？

Hey there! Let’s clear up this confusion for you—your current understanding isn’t quite right, so let’s break it down step by step.

First, let’s recap what’s happening in your code: hashlib.sha1(x) creates a SHA-1 hash object that computes the hash of your input x. The digest() method extracts the final hash result from that object—but it doesn’t convert it to a string. Instead, it returns the hash as a raw binary bytes object.

What’s the difference between digest() and hexdigest()? #

To make this concrete, here’s a quick example:

import hashlib
sample_input = b"my_training_data"
hash_obj = hashlib.sha1(sample_input)

# Using digest() returns a bytes object (raw binary data)
print(hash_obj.digest())
# Output: b'\x9d\x1f\x8a...' (exact value depends on input, but it's compact binary)

# Using hexdigest() returns a human-readable hexadecimal string
print(hash_obj.hexdigest())
# Output: '9d1f8a...' (a 40-character string, since SHA-1 produces 20 bytes, each represented by 2 hex chars)

Why use digest() in your code? #

The main reasons to choose digest() over hexdigest() are:

• Efficiency: Binary data takes up half the space of its hexadecimal string equivalent. For a SHA-1 hash, digest() gives you a 20-byte object, while hexdigest() gives you a 40-character string (which uses 40 bytes in UTF-8). If you’re hashing a large training dataset, this adds up to significant memory/storage savings.
• Compatibility: Some systems or libraries expect hash values in raw binary form (e.g., certain databases, low-level data processing tools). Using digest() ensures you’re providing the format those systems need.
• Speed: Comparing binary bytes is slightly faster than comparing strings, which can be helpful if you’re checking hash matches frequently with your training dataset hashes.

To confirm: #

If your goal was to get a string representation of the hash, you’d want to use hexdigest() instead. But in your code, digest() is being used to get the compact, raw binary version of the SHA-1 hash.

内容的提问来源于stack exchange，提问作者ironman