{"id":115,"date":"2024-01-25T11:15:21","date_gmt":"2024-01-25T11:15:21","guid":{"rendered":"https:\/\/learnpython.elegantwallp.com\/?p=115"},"modified":"2024-01-25T11:15:22","modified_gmt":"2024-01-25T11:15:22","slug":"python-tryexceptelse","status":"publish","type":"post","link":"https:\/\/learnpython.elegantwallp.com\/2024\/01\/25\/python-tryexceptelse\/","title":{"rendered":"Python try\u2026except\u2026else"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you\u2019ll learn how to use the Python try...except...else<\/code> statement.<\/p>\n\n\n\n

Introduction to the Python try\u2026except\u2026else statement<\/h2>\n\n\n\n

The\u00a0try<\/code>\u00a0statement has an optional\u00a0else<\/code>\u00a0clause with the following syntax:<\/p>\n\n\n\n

try: # code that may cause errors<\/em> except: # code that handle exceptions<\/em> else: # code that executes when no exception occurs<\/em> <\/code>Code language: PHP (php)<\/small><\/code><\/pre>\n\n\n\n
The try...except...else<\/code> statement works as follows:<\/p>\n\n\n\n
    \n
  • If an exception occurs in the try<\/code> clause, Python skips the rest of the statements in the try<\/code> clause and the except<\/code> statement execute.<\/li>\n\n\n\n
  • In case no exception occurs in the try<\/code> clause, the else<\/code> clause will execute.<\/li>\n<\/ul>\n\n\n\n
    When you include the\u00a0finally<\/code>\u00a0clause, the\u00a0else<\/code>\u00a0clause executes after the\u00a0try<\/code>\u00a0clause and before the\u00a0finally<\/code>\u00a0clause.<\/p>\n\n\n\n
    Python try\u2026except\u2026else statement examples<\/h2>\n\n\n\n
    Let\u2019s take some examples of using the try...except...else<\/code> statement.<\/p>\n\n\n\n
    1) Using try\u2026except\u2026else statement for control flow<\/h3>\n\n\n\n
    The following example illustrates how to use the try...except...else<\/code> clause develop a program that calculates the body mass index (BMI).<\/p>\n\n\n\n
    First, define a function for calculating the (BMI) based on height and weight:<\/p>\n\n\n\n
    def calculate_bmi(height, weight): \"\"\" calculate body mass index (BMI) \"\"\" return weight \/ height**2 <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Second, define another function for evaluating BMI:<\/p>\n\n\n\n
    def evaluate_bmi(bmi): \"\"\" evaluate the bmi \"\"\" if 18.5 <= bmi <= 24.9: return 'healthy' if bmi >= 25: return 'overweight' return 'underweight' <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    Third, define a new\u00a0main()<\/code>\u00a0function that prompts users for entering height and weight, and prints out the BMI result:<\/p>\n\n\n\n
    def main(): try: height = float(input('Enter your height (meters):')) weight = float(input('Enter your weight (kilograms):')) except ValueError as error: print('Error! please enter a valid number.') else: bmi = round(calculate_bmi(height, weight), 1) evaluation = evaluate_bmi(bmi) print(f'Your body mass index is {bmi}') print(f'This is considered {evaluation}!') <\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    The main()<\/code> function uses the try...except...else<\/code> statement to control its flow. If you enter height and weight that cannot be converted to numbers, the ValueError<\/code> exception will occur.<\/p>\n\n\n\n
    If no exception occurs, the else<\/code> clause will execute. It calculates the BMI index and displays the evaluation.<\/p>\n\n\n\n
    Put it all together.<\/p>\n\n\n\n
    def calculate_bmi(height, weight): \"\"\" calculate body mass index (BMI) \"\"\" return weight \/ height**2 def evaluate_bmi(bmi): \"\"\" evaluate the bmi \"\"\" if 18.5 <= bmi <= 24.9: return 'healthy' if bmi >= 25: return 'overweight' return 'underweight' def main(): try: height = float(input('Enter your height (meters):')) weight = float(input('Enter your weight (kilograms):')) except ValueError as error: print(error) else: bmi = round(calculate_bmi(height, weight), 1) evaluation = evaluate_bmi(bmi) print(f'Your body mass index is {bmi}') print(f'This is considered {evaluation}!') main()<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    2) Using Python try\u2026except\u2026else and finally example<\/h3>\n\n\n\n
    The\u00a0else<\/code>\u00a0clause executes right before the\u00a0finally<\/code>\u00a0clause if no exception occurs in the\u00a0try<\/code>\u00a0clause.<\/p>\n\n\n\n
    The following example shows how to use the\u00a0try...except...else...finally<\/code>\u00a0clause:<\/p>\n\n\n\n
    fruits = { 'apple': 10, 'orange': 20, 'banana': 30 } key = None while True: try: key = input('Enter a key to lookup:') fruit = fruits[key.lower()] except KeyError: print(f'Error! {key} does not exist.') except KeyboardInterrupt: break else: print(fruit) finally: print('Press Ctrl-C to exit.')<\/code>Code language: Python (python)<\/small><\/code><\/pre>\n\n\n\n
    How it works.<\/p>\n\n\n\n
      \n
    • First, define the fruits<\/code> dictionary that contains three elements.<\/li>\n\n\n\n
    • Second, use a while<\/code> loop to repeatedly get inputs from users. It stops the loop until the users press Ctrl-C<\/code>.<\/li>\n\n\n\n
    • Third, use the try...except...else...finally<\/code> clause inside the while<\/code> loop. We use the user input to find for the element in the dictionary.<\/li>\n<\/ul>\n\n\n\n
      If the key doesn\u2019t exist, the KeyError<\/code> exception occurs, the except clause will execute.<\/p>\n\n\n\n
      If users press Ctrl-C<\/code>, the KeyboardInterrupt<\/code> exception occurs that executes the break<\/code> statement to terminate the loop.<\/p>\n\n\n\n
      If the key is found in the fruits<\/code> dictionary, the program prints out the found element.<\/p>\n\n\n\n
      The finally<\/code> clause always executes. It shows the reminder to the users that they should press Ctrl-C to exit.<\/p>\n","protected":false},"excerpt":{"rendered":"
      Summary: in this tutorial, you\u2019ll learn how to use the Python try…except…else statement. Introduction to the Python try\u2026except\u2026else statement The\u00a0try\u00a0statement has an optional\u00a0else\u00a0clause with the following syntax: The try…except…else statement works as follows: When you include the\u00a0finally\u00a0clause, the\u00a0else\u00a0clause executes after the\u00a0try\u00a0clause and before the\u00a0finally\u00a0clause. Python try\u2026except\u2026else statement examples Let\u2019s take some examples of using the try…except…else statement. 1) Using try\u2026except\u2026else statement […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22],"tags":[],"class_list":["post-115","post","type-post","status-publish","format-standard","hentry","category-8-exception-handling"],"_links":{"self":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/115","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/comments?post=115"}],"version-history":[{"count":1,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/115\/revisions"}],"predecessor-version":[{"id":116,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/posts\/115\/revisions\/116"}],"wp:attachment":[{"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/media?parent=115"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/categories?post=115"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/learnpython.elegantwallp.com\/wp-json\/wp\/v2\/tags?post=115"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}