Tag: bugs

software engineering

The Thing about Mutable Default Arguments in Python

Dominik Muhs

Yesterday I stumbled across some code like this… def search_children(statespace, node, start_index=0, depth=0, results=[]): if depth < MAX_SEARCH_DEPTH: n_states = len(node.states) if n_states > start_index: for j in range(start_index, n_states): if node.states[j].get_current_instruction()['opcode'] == 'SSTORE': results.append(node.states[j].get_current_instruction()['address']) ... The semantics of the code don’t really matter here. Still spot the bug? It’s a very common Python gotcha… Continue reading The Thing about Mutable Default Arguments in Python