Question 5.18: Running Commands Conditionally You want to run some Python c......
Running Commands Conditionally
You want to run some Python commands only when some condition is true.
Use the Python if command.
The following example will print the message x is big only if x has a value greater than 100:
| >>> x = 101 >>> if x > 100: … print(“x is big”) … x is big |
Discussion
After the if keyword, there is a condition. This condition often, but not always, compares two values and gives an answer that is either True or False. If it is True, then the subsequent indented lines will all be executed.
It is quite common to want to do one thing if a condition is True and something different if the answer is False. In this case, the else command is used with if, as shown in this example:
| x = 101 if x > 100: print(“x is big”) else: print(“x is small”) print(“This will always print”) |
You can also chain together a long series of elif conditions. If any one of the conditions succeeds, then that block of code is executed, but none of the other conditions are tried. For example:
| x = 90 if x > 100: print(“x is big”) elif x < 10: print(“x is small”) else: print(“x is medium”) |
This example will print x is medium.
See Also
See Recipe 5.18 for more information on different types of comparisons you can make.