Mining bitcoin by different users

I am developing a blockchain using python. Here is the constructor of the Block class

class Block:
    def __init__(self, timestamp, prev_hash, data, present_hash, nonce, difficulty):
        self.timestamp = timestamp
        self.prev_hash = prev_hash
        self.data = data
        self.present_hash = present_hash
        self.nonce = nonce
        self.difficulty = difficulty

and here is the method to extract the block

@staticmethod
    def mine_block(prev_block, data):
        nonce = 0
        difficulty = prev_block.difficulty

        print('Mining in progress......')

        while True:
            nonce += 1
            timestamp = time()
            difficulty = Block.adjust_difficulty(prev_block, timestamp)

            new_hash = Block.gen_hash(timestamp, prev_block.present_hash, data, nonce, difficulty)

            if new_hash[:difficulty] == '0'*difficulty:
                break

        print('Mining is complete.')
        return Block(timestamp, prev_block.present_hash, data, new_hash, nonce, difficulty)

To resolve its difficulty I use

@staticmethod
    def adjust_difficulty(block, timestamp):
        if timestamp - float(block.timestamp) < MINE_RATE:
            return block.difficulty + 1 
        else:
            return block.difficulty - 1 

I keep constant data to extract the block. However, every time I mine the block I get a different hash. Indeed, the difficulty of announcement and the timestamp will always change.

Question:

1. How to know which hash is correct if multiple miners generated a different hash for the same data.
2. If I can figure out the number of leading zeros in the hash (difficult in my case), then why bother running the code. Why not just give it a go and give it a try. Suppose you start with 0xxx .. then 00xx, 000x, 0000, …… One of them should extract the block. If the hash length is 32. Then you will need 32 tries to break it.

PS I am new to Blockchain.