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
else:
    blockifNOexceptionisthrown

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

except NameError

The variable does not exist

except KeyError

The key does not exist in the dict

except IndexError

The index does not exist in the list