Conditionals

Programming basics

Programs generally run from the "top down". A computer will read line one, execute line one, and then go to line two, for example. It is common to include conditional statements to decide if a program should "do something else" if a specific condition is true or false.

A conditional statement evaluates an expression and executes instructions depending on the outcome of the evaluation. Conditionals depend on operators to evaluate if an expression is true or false. A condition and selection are not the same thing. A condition asks a question. A selection processes the answer.

With gratitude to and permission from Stephen Hughes (Coe College) and Philip East (University of Northern Iowa), The list below is an example of types of conditional questions. You should start thinking about conditions in plain english before you start thinking about operators.

• Match
• Threshold
• Range
• One-of
• Not-match
• Not one of
• All of
• Some of
• Eligible

Conditional operators

• Please see this link for conditional operators

Conditional code sample

# this file helps us to understand conditionals in Python.
# what do you think the output will be when you execute these instructions? 

a = 5
b = "bar"

if a == 5:
    print("Yes, the variable a has been assigned to the value 5.")
else:
    print("No, the variable a has not been assigned to the value 5.")


# what do you think the output will be when you execute these instructions? 

a = 5
b = "bar"

if b == "foo":
     print("yes, the variable b has been assigned the value foo")
else:
     print("no, the variable b has been assigned to some other value than foo.")

Multiple conditionals code sample

# this file helps us to understand multiple conditionals in Python.
# what do you think the output will be when you execute these instructions? 

a = 5
b = "bar"

if (a == 5 and b == "bar"):
    print("both conditions are true.")
else:
    print("one or both of the conditions are false")


# what do you think the output will be when you execute these instructions? 

a = 5
b = "bar"

if (a == 5 or b == "bar"):
    print("both conditions are true.")
else:
    print("one or both of the conditions are false")

Conditional code sample with lists

# this file helps us to understand conditionals in Python.
# what do you think the output will be when you execute these instructions? 

myList = ["foo","bar","baz"]

if "foo" in myList:
     print("Foo is in the list")
else:
     print("Foo is not in list")


# what do you think the output will be when you execute these instructions? 

myList = ["foo","bar","baz"]

if "bar" not in myList:
     print("bar is in the list")
else:
     print("bar is not in list")

See Also

• Operators

Assess the implications and limitations; make judgments about the ideas, works, solutions or methods in relation to selected criteria.

Give a sequence of brief answers with no explanation.