Control Flow

Control Flow

Table of Contents:

• Conditional Execution

  • Alternative Execution
  • Shortcut for Conditionals
  • Multiway Branching

• Loops: Repeated Actions

  • Repeating n times
  • Loop based on a condition

• Interpreter executes statements from top to bottom.

• Function definitions are "digested" for future fuse.

Control Flow: determines order in which statements are executed.

• Conditional Execution.
• Repeated execution - loops.
• Function definitions.

Conditional Execution

if(condition):
    statement_1! # Execute conditionally
statement_2 # Executed in flow, not a part of the if condition

• Second condition is executed only if the condition is True.
• Use uniform indentation to construct body of the conditional.

Alternative Execution

if(condition):
    statement_1
else:
    statement_2

If condition is True, then statement_1 is executed and if it is not, then statement_2 is executed.

Shortcut for conditional

• Numeric value 0 is treated as False.
• Empty sequence, "", [] is treated as False.
• Everything else is True.

Multiway branching

if(condition):
    statement_1
elif(condition):
    statement_2
elif(condition):
    statement_3
else:
    statement_4

• When check is being done for multiple conditions. elif helps evaluate multiple conditions and executes the statement within it and then exits the conditional flow.

Loops: Repeated actions

Repeat something a fixed number of times. Indentation is used for marking the body of the loop.

for i in [1,2,3,5]:
    y = y*i
    z = i + 1

Repeating n times

• Fixed loops, do something for a fixed amount of time.
• But usually, there will be cases where looping is required n number of times.
• Use range(0,n). Returns a list of numbers from 0 to n.

for i in range(0,n):
    statements

Loop based on a condition

while(condition):
    statements

• Execute body if condition evaluates to True.
• After each iteration condition is checked again.
• Body must ensure loops moves towards termination.