Python Control Flow: Managing Program Execution

By default, the instructions in a computer program are executed in a sequential manner, from top to bottom, or from start to end. However, such sequentially executing programs can perform only simplistic tasks. We would like the program to have a decision-making ability, so that it performs different steps depending on different conditions.

Most programming languages including Python provide functionality to control the flow of execution of instructions. Normally, there are two type of control flow statements.

Decision-making − The program is able to decide which of the alternative group of instructions to be executed, depending on value of a certain Boolean expression.

The following diagram illustrates how decision-making statements work −

Looping or Iteration − Most of the processes require a group of instructions to be repeatedly executed. In programming terminology, it is called a loop. Instead of the next step, if the flow is redirected towards any earlier step, it constitutes a loop.

The following diagram illustrates how the looping works −

If the control goes back unconditionally, it forms an infinite loop which is not desired as the rest of the code would never get executed.

In a conditional loop, the repeated iteration of block of statements goes on till a certain condition is met.

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