Page - 110 - in Programming for Computations – Python - A Gentle Introduction to Numerical Simulations with Python 3.6, Volume Second Edition

110 5 SomeMorePythonEssentials Ifwe try touseanuninitializedvariable, aNameErrorexception is raised: In [1]: print(x) # x is uninitialized ... ... NameError: name ’x’ is not defined Whendivisionbyzero is attempted, it results inaZeroDivisionErrorexception: In [2]: 1.0/0 ... ... ZeroDivisionError: float division by zero Using illegal indicescausesPython to raise anIndexErrorexception.: In [3]: x = [7, 8, 9] In [4]: x[2] Out[4]: 9 In [5]: x[3] # legal indices are 0, 1 and 2 ... ... IndexError: list index out of range WrongPythongrammar,orwrong typingof reservedwords,givesaSyntaxError exception: In [6]: impor numpy as np # typo... missing t in import ... impor numpy as np ^ SyntaxError: invalid syntax Ifobject typesdonotmatch,PythonraisesaTypeErrorexception: In [7]: ’a string’ + 1 # attempt to add string and integer ... ... TypeError: must be str, not int (We might add that, in the last example here, two strings could have been straight forwardlyconcatenatedwith+.) AbortExecutionwithsys.exit In some cases, it is desirable to stop execution there and then. This may be done effectively by use of the exit function in the sys modulea (a module with functions and parameters that are specific to the system). For anapplicationofsys.exit, see Sect. 7.2.2. a https://docs.python.org/3/library/sys.html. We have been careful to check code behavior in a step-wise fashion while developing our program. Still, testing should be done also with (what, for now, is regardedas) the “final” version.To test our times tables program,we should check