<p>Conditional statements in Python control program flow through if, elif and else. 1. If is used to check the condition. If it is true, the corresponding code block is executed. For example, if age >= 18 is output "You are an adult." is output; 2. elif is used to add additional conditions to judge, check in order, and no longer continue after any condition is met. For example, if score >= 80 is output "Grade: B" is output; 3. else is used to deal with uncovered remaining situations, such as if the temperature is between 10 and 30 is output "The weather is pleasant."; 4. Conditions can be used in nesting, but the hierarchy should be avoided, and or simplified logic should be given priority. Using these keywords correctly can improve code readability and maintenance. </p> <p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/175035209219669.jpg" class="lazy" alt="How do I use conditional statements in Python (if, elif, else)?"></p> <p> You use conditional statements in Python to control the flow of your program based on certain conditions. The main keywords involved are <code>if</code> , <code>elif</code> , and <code>else</code> . These let you run different blocks of code depending on whether a condition is true or false.</p> <p> Let's break down how to use them effectively.</p> <hr> <h3 id="Basic-structure-of-an-if-statement"> Basic structure of an if statement</h3> <p> At its core, an <code>if</code> statement checks if something is true. If it is, the code inside that block runs. Here's a simple example:</p><pre class='brush:php;toolbar:false;'> age = 18 if age >= 18: print("You are an adult.")</pre><p> In this case, since <code>age</code> is 18, the condition evaluates to <code>True</code> , so the message gets printed.</p><p> Keep in mind:</p><ul><li> Indentation matters in Python — everything under the <code>if</code> line must be indented consistently.</li><li> You can use comparison operators like <code>==</code> , <code>!=</code> , <code>></code> , <code><</code> , etc., inside the condition.</li></ul><hr /><h3 id="Adding-elif-for-multiple-conditions"> Adding elif for multiple conditions</h3><p> What if you want to check more than one possibility? That's where <code>elif</code> comes in. It stands for “else if,” and lets you chain additional conditions.</p><p> For example:</p><pre class='brush:php;toolbar:false;'> score = 85 if score >= 90: print("Grade: A") elif score >= 80: print("Grade: B") elif score >= 70: print("Grade: C")</pre><p> This will print <code>"Grade: B"</code> because the first condition fails (not ≥90), but the second one passes (≥80).</p><p> A few things to remember:</p><ul><li> You can have as many <code>elif</code> blocks as needed.</li><li> Each condition is checked in order — once one passes, the rest are skipped.</li><li> It helps avoid deeply nested logic by keeping things flat and readable.</li></ul><hr /><h3 id="Using-else-as-a-fallback"> Using else as a fallback</h3><p> If none of the earlier conditions are met, the <code>else</code> block runs. It acts as a default case.</p><p> Here's a full example with all three parts:</p><pre class='brush:php;toolbar:false;'> temperature = 25 if temperature > 30: print("It&#39;s hot outside.") elif temperature < 10: print("It&#39;s cold.") else: print("The weather is pleasant.")</pre><p> Since 25 is neither above 30 nor below 10, the output will be <code>"The weather is pleasant."</code></p><p> Use <code>else</code> when you want to handle any leftover cases. Just make sure it's not doing too much — sometimes explicitly listing all conditions is clearer.</p><hr /><h3 id="Nesting-conditions"> Nesting conditions</h3><p> Sometimes you need to check another condition inside an existing one. This is called nesting.</p><p> Example:</p><pre class='brush:php;toolbar:false;'> user_role = "admin" logged_in = True if logged_in: if user_role == "admin": print("Welcome, admin!") else: print("Welcome, user!") else: print("Please log in.")</pre><p> In this case, we first check if the user is logged in. Only then do we look at their role.</p> <p> When nesting:</p> <ul> <li> Keep it shallow — too many levels get confusing fast.</li> <li> Think about whether you can simplify using <code>and</code> or <code>or</code> instead.</li> </ul> <hr> <p> That's basically how you work with conditions in Python. They're straightforward but powerful, and knowing how to combine them cleanly make your code easier to read and maintain.</p>

The above is the detailed content of How do I use conditional statements in Python (if, elif, else)?. For more information, please follow other related articles on the PHP Chinese website!