Use birthday attack to find hash collision (Python)

Background: use SHA-1 as hashing method, but only use last 6-bytes as digest. The objectives are related to find the collision of this digest. (last 6-byte as digest for all part 1 to part 3) Part 1: find any x1 and x2, such that H(x1) = H(x2). I will provide a algorithm (with constant storage to store hash values) later. Part 2: similar as Part 1, but x1 and x2 should be ASCII numeric string (e.g. 123344...). Find the collision (last 6 bytes as digest). Instead of brute-force, I will suggest you a reduce function later. Part 3: I will give you two html files. They have different hash digest. You can add comments at the end of file, such that revised two files have collision (last 6-byte as digest). I will introduce you the digest function, same as Part 2. Remarks: 1. The key point is birthday attack, instead of exploiting vulnerability of hash algorithm (e.g. SHA1 in this case). It is how to implement this birthday attack. 2. Normal computer's computation capability is enough to handle these in short time. 3. Make sure you utilize less than 10M memory, and also return the running time of finding collision. I will send more details over private chat. 3-4 days should be enough for this.