{"id":16429,"date":"2020-10-22T04:21:41","date_gmt":"2020-10-22T11:21:41","guid":{"rendered":"https:\/\/careerkarma.com\/blog\/?p=16429"},"modified":"2023-12-01T04:03:21","modified_gmt":"2023-12-01T12:03:21","slug":"python-if-else","status":"publish","type":"post","link":"https:\/\/careerkarma.com\/blog\/python-if-else\/","title":{"rendered":"if else Python Statements: A Step-By-Step Guide"},"content":{"rendered":"\n

An if else Python statement evaluates whether an expressio<\/em>n is tr<\/em>ue or false. If a conditio<\/em>n is tr<\/em>ue, the “if” statement executes. Otherwise, the “else” statement executes. Python if else statements help coders control the flow of their programs.<\/em><\/p>\n\n\n\n

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When you\u2019re writing a program, you may want a block of code to run only when a certain condition is met. That\u2019s where conditional statements come in. Conditional statements allow you to control the flow of your program more effectively. <\/p>\n\n\n\n

In Python, the if<\/em> and if…else<\/em> statements are used to perform conditional operations. This tutorial will discuss, with reference to examples, the basics of the if<\/em>, if…else<\/em>, and elif<\/em> statements in Python. We\u2019ll also discuss how to use nested if<\/em> statements.<\/p>\n\n\n\n

Python if Statement<\/h2>\n\n\n\n

A Python if statement evaluates whether a condition is equal to true or false. The statement will execute a block of code if a specified condition is equal to true. Otherwise, the block of code within the if statement is not executed.<\/p>\n\n\n\n

Let’s write a program that prints the price of a sandwich order. The price of a sandwich order should only be displayed if the customer has ordered a ham roll. Our sandwich order is a Python string<\/a>. Here’s the code for our program:<\/p>\n\n\n\n

sandwich_order = "Ham Roll"\n\nif sandwich_order == "Ham Roll":\n\tprint("Price: $1.75")<\/pre><\/div>\n\n\n\n
Our code returns: Price: $1.75<\/code><\/p>\n\n\n\n
We have declared a variable called sandwich_order. This variable has been assigned the value Ham Roll<\/em>.\n\n<\/p>\n\n\n\n
We use an if<\/em> statement to check whether sandwich_order is equal to Ham Roll<\/em>. If our condition is true, our print()<\/em><\/a> statement<\/a> is be executed. If our condition is false, nothing will happen.\n\n<\/p>\n\n\n\n
Our sandwich_order variable is equal to Ham Roll. <\/em>This means that our if<\/em> statement is executed. Now, let\u2019s see what happens when we change our sandwich order to Cheese Roll<\/em>:<\/p>\n\n\n\n
sandwich_order = "Cheese Roll"\n\nif sandwich_order == "Ham Roll":\n\tprint("Price: $1.75")<\/pre><\/div>\n\n\n\n
Our code returns nothing. The print()<\/em> statement in our code is not given the chance to execute. This is because our sandwich order is not equal to Ham Roll.<\/em><\/p>\n\n\n\n
if else Python Statement<\/h2>\n\n\n\n
An if…else Python statement checks whether a condition is true. If a condition is true, the if statement executes. Otherwise, the else statement executes.<\/p>\n\n\n\n
So far, we have used an if statement to test for whether a particular condition is met. But, what if we want to do something if a condition is not met?<\/p>\n\n\n\n
Suppose we are building an app that checks whether a customer at a local restaurant has run up a tab. If the customer has run up a tab over $20, they need to pay it off before they can order more food. Nothing should happen if the customer does not have a tab accrued over $20.\n\n<\/p>\n\n\n\n
To accomplish this task, we could use the following code:<\/p>\n\n\n\n
tab = 29.95\n\nif tab > 20:\n\tprint("This user has a tab over $20 that needs to be paid.")\nelse:\n\tprint("This user's tab is below $20 that does not require immediate payment.")<\/pre><\/div>\n\n\n\n
Our code returns: This user has a tab over $20 that needs to be paid.<\/em>\n\n<\/p>\n\n\n\n
Let\u2019s walk through how our code works. First, we declare a Python variable<\/a> called tab. <\/em>This variable tracks a customer\u2019s tab. We use an if<\/em> statement to check whether the customer\u2019s tab is greater than 20.<\/p>\n\n\n\n
If a customer’s tab is worth more than $20, the print()<\/em> statement after our if<\/em> statement is executed. Otherwise, the print()<\/em> statement after our Python if\u2026else clause is executed.\n\n<\/p>\n\n\n\n
Because our customer\u2019s tab is over $20, the Python interpreter<\/a> executes our if statement. This instructs our program to print a message to the console. The message tells us that the customer must pay their tab.\n\n<\/p>\n\n\n\n
Let’s set the customer’s tab to $0 and see what happens:<\/p>\n\n\n\n
This user's tab is below $20 which does not require immediate payment.<\/pre><\/div>\n\n\n\n
Our code returns a different output. The customer\u2019s tab is not over $20. This means the contents of our else<\/em> statement are executed instead of our if<\/em> statement. <\/p>\n\n\n\n
Python elif Statement<\/h2>\n\n\n\n
A Python elif statement checks for another condition if all preceding conditions are not met. They appear after a Python if statement and before an else statement. You can use as many elif statements as you want.<\/p>\n\n\n\n
In our above example, we created a conditional statement with two possible outcomes. If the user\u2019s tab was over $20, a message was printed to the console. If a user\u2019s tab was under $20, a different message was printed to the console.<\/p>\n\n\n\n
In some cases, we may want to evaluate multiple conditions and create outcomes for each of those conditions. That\u2019s where the elif<\/em> condition comes in.<\/p>\n\n\n\n
elif Python Statement Example<\/h3>\n\n\n\n
Let\u2019s return to our sandwich example from earlier. Suppose we want to have four potential outputs from our program, depending on the sandwich filling a customer chooses. These are:\n\n<\/p>\n\n\n\n
  • Ham Roll: $1.75<\/li>
  • Cheese Roll: $1.80<\/li>
  • Bacon Roll: $2.10<\/li>
  • Other Filled Roll: $2.00<\/li><\/ul>\n\n\n\n
    We could use the following code to calculate the cost of the customer\u2019s order:<\/p>\n\n\n\n
    sandwich_order = "Bacon Roll"\n\nif sandwich_order == "Ham Roll":\n\tprint("Price: $1.75")\nelif sandwich_order == "Cheese Roll":\n\tprint("Price: $1.80")\nelif sandwich_order == "Bacon Roll":\n\tprint("Price: $2.10")\nelse:\n\tprint("Price: $2.00")<\/pre><\/div>\n\n\n\n
    Our code returns: Price: $2.10<\/code>.<\/p>\n\n\n\n
    Our code has four possible outcomes:<\/p>\n\n\n\n
    • If a customer orders a ham roll, the contents of the \u201cif\u201d statement are executed. This prints \u201cPrice: $1.75\u201d to the console.<\/li>
    • If a customer orders a cheese roll, the contents of the first \u201celif\u201d statement are executed. This prints \u201cPrice: $1.80\u201d to the console.<\/li>
    • If a customer orders a bacon roll, the contents of the second \u201celif\u201d statement are run. This prints \u201cPrice: $2.10\u201d to the console.<\/li>
    • We display \u201cPrice: $2.10\u201d on the console if a customer orders a roll with a different filling.<\/li><\/ul>\n\n\n\n
      We used an if<\/em> statement to test for a specific condition. Our two elif<\/em> blocks to test for alternative conditions. The else<\/em> statement returns a value in case no conditions are met.\n\n<\/p>\n\n\n\n
      We could add in more elif<\/em> statements to our above code if we wanted. If we introduced a new Tuna Roll<\/em> to our sandwich menu, we could add in a new elif<\/em> statement. This new statement could print the price of the new menu item to the console.<\/p>\n\n\n\n
      Python Nested if Statements<\/h2>\n\n\n\n
      A nested if statement is an if statement inside another if statement. Nested if statements let you check if a condition is met after another condition has already been met.<\/p>\n\n\n\n
      Let\u2019s return to our sandwich example from earlier. Suppose we want to check whether a customer has ordered a roll that is on our menu. We want to do this before we check the prices of the customer\u2019s order.<\/p>\n\n\n\n
      Python Nested if Statement Example<\/h3>\n\n\n\n
      A message should be printed to the screen with our default price for non-menu items if a customer has ordered another custom<\/em> sandwich. Custom sandwiches are sandwiches that are not on our menu (such as a buttered roll, or a jam roll).<\/p>\n\n\n\n
      However, if a customer has ordered a sandwich that is on our menu, we should then check to see the price of that sandwich. We could do so using this code:<\/p>\n\n\n\n
      sandwich_order = "Other Filled Roll"\n\nif sandwich_order != "Other Filled Roll":\n\n\tif sandwich_order == "Ham Roll":\n\tprint("Price: $1.75")\nif sandwich_order == "Cheese Roll":\n\tprint("Price: $1.80")\nelif sandwich_order == "Bacon Roll":\n\tprint("Price: $2.10")\n\nelse:\n\tprint("Price: $2.00")<\/pre><\/div>\n\n\n\n
      Our code returns: Price: $2.00<\/code>. <\/p>\n\n\n\n
      First, our program evaluates whether our sandwich order is not equal to Other Filled Roll<\/em>. Our program will compare the sandwich we have ordered with the list of sandwiches on our menu. This happens if we have ordered a sandwich on the menu.\n\n<\/p>\n\n\n\n
      If we have ordered a filled roll that is not on our menu, the contents of the else<\/em> statement in our code are executed.\n\n<\/p>\n\n\n\n
      In this example, we have ordered a filled roll that is not on our menu. This means that the statement if sandwich_order != Other Filled Roll<\/em> evaluates to False, so the code in our if statement is executed.\n\n<\/p>\n\n\n\n
      Now, suppose we ordered a ham roll instead. This would cause our first if<\/em> statement to evaluate to true. This is because Ham Roll<\/em> is not equal to Other Filled Roll. <\/em>Our order will be compared to the list of sandwich prices we have specified.<\/p>\n\n\n\n
      View the Repl.it from this tutorial:<\/strong> <\/p>\n\n\n\n