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      Control FlowBreak StatementContinue StatementPass StatementNested LoopsDecision MakingIf StatementIf-else StatementNested IF StatementMatch-Case StatementLoopsFor LoopsFor-else LoopsWhile Loops

      FunctionsBuilt-in FunctionsDefault ArgumentsKeyword ArgumentsKeyword-Only ArgumentsPositional ArgumentsPositional-Only ArgumentsArbitrary ArgumentsVariable ScopeFunction AnnotationsModules

      StringSlicing StringsModify StringsString ConcatenationString FormattingEscape CharactersString MethodsString Exercises

      ListsList ExercisesAccess List ItemsChange List ItemsAdd List ItemsRemove List ItemsLoop ListsList ComprehensionSort ListsCopy ListsJoin ListsList Methods

      TuplesAccess Tuple ItemsUpdate TuplesUnpack Tuple ItemsLoop TuplesJoin TuplesTuple MethodsTuple Exercises

      SetsAccess Set ItemsAdd Set ItemsRemove Set ItemsLoop SetsJoin SetsCopy SetsSet OperatorsSet MethodsSet Exercises

      DictionariesDictionary ExercisesAccess Dictionary ItemsChange Dictionary ItemsAdd Dictionary ItemsRemove Dictionary ItemsDictionary View ObjectsLoop DictionariesCopy DictionariesNested DictionariesDictionary Methods

      ArraysAccess Array ItemsAdd Array ItemsRemove Array ItemsLoop ArraysCopy ArraysReverse ArraysSort ArraysJoin ArraysArray MethodsArray Exercises

      File HandlingWrite to FileRead FilesRenaming and Deleting FilesDirectoriesFile Methods

      OOP ConceptsDynamic BindingDynamic TypingAbstractionObject and ClassesEncapsulationInterfacesPackagesInner ClassesAnonymous Class and ObjectsSingleton ClassWrapper ClassesEnumsReflectionClass AttributesClass MethodsStatic MethodsConstructorsAccess ModifiersInheritancePolymorphismMethod OverridingMethod Overloading

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      Control Flow

      Python Tutorial

      This Python tutorial has been written for the beginners to help them understand the basic to advanced concepts of Python Programming Language. After completing this tutorial, you will find yourself at a great level of expertise in Python, from where you can take yourself to the next levels to become a world class Software Engineer.

      Control Flow

      Python program control flow is regulated by various types of conditional statements, loops, and function calls. 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 in any programming language and Python also supports them.

      Decision-making Statements

      Decision making statements are used in the Python programs to make them 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
      

      The if Statement

      Python provides if..elif..else control statements as a part of decision marking. Following is a simple example which makes use of if..elif..else. You can try to run this program using different marks and verify the result.
      marks = 80 
      result = ""
      if marks < 30:
         result = "Failed"
      elif marks > 75:
         result = "Passed with distinction"
      else:
         result = "Passed"
      
      print(result)
      This will produce following result:
      Passed with distinction

      The match Statement

      Python supports Match-Case statement, which can also be used as a part of decision making. Following is a simple example which makes use of match statement.
      def checkVowel(n):
         match n:
            case 'a': return "Vowel alphabet"
            case 'e': return "Vowel alphabet"
            case 'i': return "Vowel alphabet"
            case 'o': return "Vowel alphabet"
            case 'u': return "Vowel alphabet"
            case _: return "Simple alphabet"
      print (checkVowel('a'))
      print (checkVowel('m'))
      print (checkVowel('o'))
      This will produce following result:
      Vowel alphabet
      Simple alphabet
      Vowel alphabet

      Loops or Iteration Statements

      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. Python supports a number of loops like for loop, while loop which we will study in next chapters.

      The for Loop

      Following is an example which makes use of For Loop to iterate through an array in Python:
      words = ["one", "two", "three"]
      for x in words:
        print(x)
      This will produce following result:
      one
      two
      three

      The while Loop

      Following is an example which makes use of While Loop to print first 5 numbers in Python:
      i = 1
      while i < 6:
        print(i)
        i += 1
      This will produce following result:
      1
      2
      3
      4
      5

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.