produce a range of numbers
|Use:||range( first, last, inc )
|Description:||Used in the for command to produce a sequence (range) of numbers.|
|Parameters:||first||Optional, sets the first number in the sequence, If this parameter is not present, the first number is 0|
|last||Required, sets the last number in the sequence. (note that the loop will stop one before this number)|
|inc||Optional, only used if 3 parameters are present. It specifies the increment value, it can be positive or negative, but it should not be set to 0.|
|Related:||for, break, continue|
The range command is used with the for command to run a block of code multiple times.
Each time the for command runs through its loop, the range command is used to give the loop variable a new number. The parameters for the range command are used to set the number of times the loop runs, the first , last and increment value of the loop variable.
In the simplest form the range command uses 1 parameter e.g. range( num ). Used in a for loop this will repeat the loop num times.
for a in range(10): # do 10 times print 'the value of a is', a
the value of a is 0 the value of a is 1 the value of a is 2 the value of a is 3 the value of a is 4 the value of a is 5 the value of a is 6 the value of a is 7 the value of a is 8 the value of a is 9
Note: that in this example the loop runs 10 times, the loop variable a starts with value 0 and increments by 1 each time, but it ends with the loop variable a equal to 9 (the loop variable a never gets to 10). This catches a lot of people out.
When the range command is used with 2 parameters, it defines the first and last values of the loop variable.
for b in range(6,10): print 'the value of b is', b
the value of b is 6 the value of b is 7 the value of b is 8 the value of b is 9
This runs the loop 4 times, with b starting at 6 and finishing at 9.
When the range command is used with 3 parameters the first, last and the increment are defined.
for c in range(6,10,2): print 'the value of c is', c
the value of c is 6 the value of c is 8
Using a negative increment value the loop variable will decrease each time round the loop.
for d in range(4,0,-1): print 'the value of d is', d
the value of d is 4 the value of d is 3 the value of d is 2 the value of d is 1
In this loop it only goes 4 times round the loop and the loop variable d never gets to 0