Python:Control structures

Most flow control is standard. Indentation defines the code block to execute. You must be strict, all indents must be the same in a block, a mix of spaces and tabs is not allowed (unless each line uses the same mix).

if expression:
    block
else:
    otherblock

pass

No operation, use e.g. to avoid negative tests

Exception handling

To catch exceptions:

try:
    blockthatmaythowexception
except <exception>:
    blockifexceptionisthrown

Specifying an exception is optional but highly recommended. The exceptiontypes can be found in the python docs

except NameError

The variable does not exist