Input and Output

Output

Python uses print() to print output text or values to the console. print() in Python inserts a new line at the end of the output and insert a whitespace to separate each element automatically.

Syntax:

            

            
    print("Some random text")
    print(variable_name1, variable_name2) 
            
          


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In Python, when we want to print int type of variable together with string, we have to type cast it into str first, so that it can be printed. Another way is to use the f operator and format function.

            

            
  print("Some text has " +  str(other_variable) + " length")
  print(f"Some text has {other_variable} length")
  print("Hello {} {}, hope you're well!".format(variable1, variable2))   
            
          


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If we don't want Python to automatically insert a new line after each line printed or insert a white space to separate the variables, we can specify it using end="...", sep="..." in the print statement. If not, then Python will automatically set end="\n" and sep=" ". In Python, the double quote and the single quote can both be used to define string. \n is an escape sequence used to insert a new line.

Syntax: print(variable_name1, variable_name2, end=" ", sep="")

Example:

            

            
    myAge = 18
    yourAge = 20
    
    print("Hello World", "bye")
    print('Hello World', 'bye', end="", sep="\n")
    
    print("\nI am " + str(myAge) + " years old")
    print(f"You are {yourAge} years old")
    print("The ages are {} and {}.".format(myAge, yourAge))
            
          


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Output:

               

               
    Hello World bye
    Hello World
    bye
    I am 18 years old
    You are 20 years old
    The ages are 18 and 20.
               
             
             

Input

In Python, you can use the input function to get user input. Note that if we don't typecast the input, then it will automatically be treated as a string by Python.

Syntax: variable_name = input("Enter a string: ")

            

            
    #input is treated as string
    myNum = input("Enter a number: ") 

    #input is treated as int
    myNum2 = int(input("Enter a number: "))
            
          


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Comments

Comments can be used to explain what does a block of code do. Comments can also be used to prevent the execution of some lines of code. Python comment is a single line.

Syntax: #some comment here
Any text between # and the end of the line will not be executed by the compiler.

            

            
    #this line will not be executed
    myNum = input("Enter a number: ")
    print(myNum)
    
    #print("hello")
    #"hello" will not be printed out because
    #it is in the comment block.
            
          


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Escape Sequences

Escape sequences are mostly used to control or format the output. It started with a backslash (\) and followed by another character.

            

            
    print("Hello,\nWorld!");

    #The output will be
    #Hello,
    #World!
    #Instead of 
    #Hello,World!     
            
          


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Below are the most commonly used escape sequences.

Exception Handling

An exception is an exceptional circumstance that appears when a program is executed. For example, division by zero, invalid inputs, and many more. Python exception handling consists of four major keywords with else and finally being optional:

• try
A try block identifies which block of code will be tested and performed exception-catching. The keyword try has to be followed by one or more except keywords to perform the exception-catching.
• except
The except keyword indicates the catching of an exception.
• else
The else keyword lets you execute code when there is no error.
• finally
The finally keyword lets you execute code regardless of the result of the exception-catching.

Syntax:

            

            
    try:
        #code block
    except error_name:
        #code block
    except:
        #code block
    else:
        #code block
    finally:
        #code block
            
          


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Example:

            

            
    try:
      print(x)
    except NameError:
      print("Variable x is not defined")
    except:
      print("Something else went wrong")
    else:
      print("Nothing went wrong")
    finally:
      print("Exception handling process is done")
            
          


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Output:

                 

                 
    Variable x is not defined
    Exception handling process is done  
                 
               
               

In this case, the variable x is not defined, so there is NameError. Therefore, the message Variable x is not defined is printed. If the error is not NameError, then the message Something else went wrong will be printed and if there is no error at all, then the message Nothing went wrong will be printed. The message in finally will always be printed regardless the result.