Conditionals

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Programming basics[1]

Programs generally run sequentially, starting from the first instruction and then moving to the next instruction, in a step-by-step process. 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)[2], 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[edit]


Conditional code sample[edit]

# 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[edit]

# 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[edit]

# 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")



Some videos[edit]



See Also[edit]

References[edit]