Python/Program Flow and Logicals

Preliminaries

One essential thing to understand when programming in Python is that correct indenting of code is essential. The Python programming language was designed with readability in mind, and as a result forces you to indent code blocks such as the following:

• while and for loops
• if, elif, else constructs
• functions

The indent for each code block must be the same, and the Python programming language also requires you to mark the start of a code block with a colon. So where MATLAB used end to mark the end of a block of code, Python uses a change in indent. Other than this, simple Python programmes aren't dissimilar to those in MATLAB.

So for example, the simplest case of an if conditional statement in Python would look something like this

if condition:
   statement1
   statement2
   ...

and the code in lines statement1, statement2, ... is executed only if condition is true. Sharp sighted readers might also spot another difference to MATLAB, in Python there is no need to add a semicolon at the end of a line to suppress output.

The if functionality can be expanded using else as follows

if condition:
   statement1
   statement2
   ...
else:
   statement1a
   statement2a
   ...

where statement1, statement2, ... is executed if condition is true, and statement1a, statement2a, ... is executed if condition is false. Note that the code block after the else starts with a colon, and the code block is also indented.

Finally, the most general form of this programming construct introduces the elif keyword (in contrast to elseif in MATLAB to give

if condition1:
   statement1
   statement2
   ...
elif condition2:
   statement1a
   statement2a
   ...
   ...
   ...
elseif conditionN:
   statement1b
   statement2b
   ...
else:
   statement1c
   statement2c
   ...