(→Flow control) |
|||

Line 22: | Line 22: | ||

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 | 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. | way to get out of that level without doing anything, and an exit() leaves the entire program. | ||

+ | |||

+ | A ''while'' statement tests whether its argument is true, and sets up a loop that continues as long as it is. Program | ||

+ | |||

+ | flag = True | ||

+ | x = 0. | ||

+ | while flag: | ||

+ | x = x + 1. | ||

+ | if x > 10.: | ||

+ | flag = False | ||

+ | print x | ||

+ | |||

+ | increases x until it is 11. and then prints the value. | ||

+ | |||

+ | |||

+ | |||

+ | |||

+ | |||

== Functions == | == Functions == |

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

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.

A *while* statement tests whether its argument is true, and sets up a loop that continues as long as it is. Program

flag = True x = 0. while flag: x = x + 1. if x > 10.: flag = False print x

increases x until it is 11. and then prints the value.

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

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