Conditional Execution in Python (Part I)
Boolean Expressions
A boolean expression is an expression that is either true or false. The following examples use the operator ==, which compares two operands and produces True if they are equal and False otherwise.
>>> 5 == 5
True
>>> 5 == 6
False
True and False are special values that belong to the type bool; they are not strings:
>>> type(True)
<type ‘bool’>
>>> type(False)
<type ‘bool’>
The == operator is one of the comparison operators; the others are:
x != y # x is not equal to y
x > y # x is greater than y
x < y # x is less than y
x >= y # x is greater than or equal to y
x <= y # x is less than or equal to y
x is y # x is the same as y
x is not y # x is not the same as y
A common error is to use a single equal sign (=) instead of a double equal sign (==). Remember that = is an assignment operator and == is a comparison operator. There is no such thing as =< or =>.
Logical Operators
There are three logical operators: and, or, and not. The semantics (meaning) of these operators is similar to their meaning in English. For example,
x > 0 and x < 10 is true only if x is greater than 0 and less than 10.
n%2 == 0 or n%3 == 0 is true if either of the conditions is true, that is, if the number is divisible by 2 or 3.
Finally, the not operator negates a boolean expression, so not (x > y) is true if x > y is false, that is, if x is less than or equal to y.
About Author
Naveed Afzal
Naveed Afzal is an Assistant Professor in Computer Science. He received his PhD degree in Computational Linguistics at the University of Wolverhampton, UK and a Master’s degree in Advanced Software Engineering at the University of Sheffield, UK. He have published many research articles in well-known conferences and journals. His research interests includes: NLP, Data Mining, Information Extraction, Sentiment Analysis, E-Learning, Corpus Linguistics and Software Engineering.
