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Solving problems with Python

From AstroEd

Revision as of 04:00, 14 February 2013 by WikiSysop (talk | contribs) (Flow control)

Now with many useful tools in hand, let us see how to make them work together to solve problems.


Flow control

The if statement is fundamental to making decisions within a program. It works simply

x=0.1
y=10.
z=0.
if x > 0.:
  y = 1./x
elif x < -1.:
  pass
elif x == 0:
  print 'Cannot divide by zero.'
  exit()
else:
  y = 1./x
z = y

Notice that indentation (by any fixed number of spaces)is used to separate the functions within the statement, and that each branch is defined by a :. The end of a branch occurs when the indentation goes back to the previous level. Each decision is based on a logical boolean value such as (x > 0.), which is True when x is greater than 0. and False otherwise. Within the if processing, a pass is a way to get out of that level without doing anything, and an exit() leaves the entire program.

Functions

Iteration

Examples

For examples of Python illustrating flow control, functions, and iteration, see the examples section.


Assignments

For the assigned homework to use these ideas, see the assignments section.