> ## Documentation Index
> Fetch the complete documentation index at: https://docs.theblockchainlibrary.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Keccak256 Hashing (Python)

> Compute Keccak-256 hashes in Python, matching Solidity's keccak256 function.

# Keccak256 Hashing (Python)

Compute Keccak-256 hashes in Python, matching Solidity's keccak256 function.

Compute Keccak-256 hashes in Python, matching Solidity's keccak256 function.

## Explanation

Keccak-256 is the hash function used by Ethereum. The first 4 bytes of keccak(signature) is the function selector used in ABI encoding. eth\_hash provides a pure-Python implementation; pysha3 is an alternative.

## Code

```python theme={null}
from eth_hash.auto import keccak

# Hash a string
data = b"Hello, World!"
h = keccak(data)
print("Hash:", h.hex())

# Hash an ABI-encoded packed message (for EIP-712)
from eth_abi.packed import encode_packed

packed = encode_packed(
    ["address", "uint256"],
    ["0x1234...address", 1000]
)
leaf = keccak(packed)
print("Leaf:", leaf.hex())

# Compute function selector
sig = "transfer(address,uint256)"
selector = keccak(sig.encode())[:4]
print("Selector:", selector.hex())  # 0xa9059cbb
```

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**Canonical knowledge ID:** `code-example:keccak256-hashing-python`