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Practice

Trace a status counter

A loop visits ["open", "closed", "open", "open"] and adds 1 only when status == "open". What final count is reported?

Python hand trace

Follow the statements that execute, one state change at a time

  1. InputsRecord initial values
  2. PathFollow indentation and branches
  3. StateRecord each assignment
  4. CallsBind arguments and trace returns
  5. OutputState the final observed value
  6. CheckRepeat the trace independently

A reliable prediction starts with inputs, respects indentation and control flow, records assignments, and separates returned values from printed output.