"if" Statement for Conditional Execution

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∟"if" Statement for Conditional Execution

This section provides a quick introduction of 'if' statement, which selects a block of sub-statements to execute based on given conditions.

What Is "if" Statement? An "if" statement is a compound statement that selects a block of sub-statements to execute based on given conditions.

An "if" statements must have an "is" clause followed by multiple optional "elif" clauses and an optional "else" clause:

if condition:
  sub-statement
  sub-statement
  ...
elif condition:
  sub-statement
  sub-statement
  ...
...
else:
  sub-statement
  sub-statement
  ...

Here is a Python sample code, if_test.py, that shows you how to use "if" statements.

#  if_test.py
#- Copyright 2011 (c) HerongYang.com. All Rights Reserved.
#
from datetime import datetime
today = datetime.now()
weekDay = today.weekday()

openHours = "open"
if weekDay == 0:
   openHours = "closed"
elif weekDay >= 1 and weekDay <= 5:
   openHours = "open from 9:00am to 9:00pm"
elif weekDay == 6:
   openHours = "open from 9:00am to 5:00pm"
else:
   openHours = "should never reach here"

print("   Today is "+today.strftime("%A"))
print("   The library is "+openHours)

If you run this sample code, you should get:

herong> python if_test.py

   Today is Saturday
   The library is open from 9:00am to 9:00pm

Note that Python uses indention to identify sub-statement blocks. There is no keywords or brackets to mark the beginning and the ending of a sub-statement block.