If Else Statements in Python | Python for Beginners

Alex The Analyst

15 Nov 202206:40

Summary

TLDRThis video explains how to use the if-elif-else statement in Python. The instructor demonstrates how to create conditional statements that check whether certain conditions are true or false, using comparison and logical operators. The video walks through writing code for various conditions, including nested if statements and one-line if-else expressions. It also highlights how the Python interpreter evaluates these conditions step-by-step. The guide aims to help viewers understand the structure and flexibility of Python's conditional statements, making it ideal for those learning programming basics.

Takeaways

😀 The video covers the if-else statement in Python programming.
🤓 The if-else statement evaluates conditions and executes a body of code if true or false.
📊 The 'elif' statement checks a secondary condition if the initial 'if' condition is false.
🔁 You can have multiple 'elif' statements, but only one 'if' and one 'else' statement in a block.
💻 An example was shown where 'if 25 is greater than 10' evaluates as true and prints 'it worked'.
🔎 If a condition in 'if' is false, the code moves to the 'else' block for execution.
📝 You can chain multiple conditions with 'elif', as demonstrated in the 25, 30, 40, and 50 comparisons.
⚙️ Logical operators like 'and' or 'or' can be used inside the condition statements for more complex logic.
🚀 Python also allows writing if-else statements in a single line for concise conditions.
🧩 Nested if statements are possible, where an if statement is placed within another, allowing more intricate decision-making.

Q & A

What is the basic structure of an if-else statement in Python?
-An if-else statement starts with an 'if' condition. If the condition is true, a block of code is executed. If it's false, the 'else' block of code runs.
What is the purpose of the 'elif' statement in Python?
-'Elif' (short for 'else if') checks another condition if the previous 'if' condition is false. You can have multiple 'elif' statements in a single if-else structure.
How many 'if' and 'else' statements can be used in a Python if-else structure?
-You can only have one 'if' statement and one 'else' statement in a structure, but you can have multiple 'elif' statements between them.
What happens when an 'if' statement's condition is true?
-If the condition is true, Python executes the block of code under the 'if' statement and skips any 'elif' or 'else' blocks.
What happens if all conditions in the if-elif structure are false?
-If all conditions in the 'if' and 'elif' statements are false, the code in the 'else' block is executed.
How does Python handle indentation in if-else statements?
-When writing an if-else statement, Python automatically indents the code inside the body of the statement after a colon (':'). Proper indentation is crucial for defining code blocks.
Can you use multiple comparison operators in an if statement?
-Yes, you can use logical operators like 'and' or 'or' to combine multiple conditions in a single if statement.
How does Python handle a one-line if-else statement?
-Python allows if-else statements to be written on one line using the syntax: 'print(output_if_true) if condition else print(output_if_false)'.
What is a nested if statement?
-A nested if statement is an if statement inside another if statement. It allows for multiple levels of condition checks, creating more complex logic.
What happens when a condition in the elif chain becomes true?
-When a condition in an 'elif' statement becomes true, its corresponding block of code is executed, and the rest of the 'elif' and 'else' statements are skipped.

Outlines

00:00

💡 Introduction to the If-Else Statement in Python

The first paragraph introduces the concept of the if-else statement in Python. The speaker explains that while it's technically called the 'if-elif-else' statement, they will refer to it simply as 'if-else'. A blurry flowchart is presented to illustrate how the if statement works. If the initial condition is true, a body of code runs; otherwise, the program moves to the elif condition. If the elif condition is true, another block of code is executed. If both conditions are false, the else statement's code runs. It is emphasized that there can only be one 'if' and one 'else' statement, but multiple 'elif' statements.

05:00

🔤 Writing the If-Else Code in Python

In this section, the speaker walks through writing an if-else statement in Python. They start with the 'if' statement, checking if 25 is greater than 10. Since the condition is true, the body of the code prints 'it worked'. Next, the speaker shows how an else statement functions by checking if 25 is less than 10, which is false, leading the program to execute the else block and print 'it did not work'. The process illustrates how Python automatically indents the code for readability, with conditions dictating which block of code is executed.

🧩 Handling Multiple Conditions with Elif

This paragraph introduces the 'elif' statement and shows how it works with multiple conditions. The speaker starts by modifying the previous code to check if 25 is less than 30 using 'elif'. When this condition is true, it prints 'elif worked'. They then demonstrate adding more 'elif' statements with different conditions (25 less than 20, 21, 40, and 50). The first 'elif' condition that evaluates as true (25 < 40) triggers the corresponding code block and prevents the subsequent elifs from running. This section shows how multiple conditions can be evaluated in sequence using 'elif'.

🔗 Using Logical Operators in If Statements

The speaker expands on the use of logical operators like 'and' and 'or' in if statements. By using multiple conditions in one if statement, such as checking whether 25 is less than 10 'or' 1 is less than 3, the code runs if at least one condition is true. They explain how logical operators can combine different conditions to evaluate the truth of an if statement. This section also touches on writing if-else statements in a single line for more concise code, although this approach limits the readability and complexity of the conditions.

🔄 Introducing Nested If Statements

In this part, the speaker explains nested if statements, where one if statement is placed inside another. They demonstrate this by creating a new condition inside an already-true if block. For example, after the first condition (25 < 10 or 1 < 3) is met, they add a nested if statement checking if 10 is greater than 5. If true, it prints another message. This concept allows for more complex decision-making, enabling multiple layers of conditions to be evaluated in sequence. Nested if statements are a powerful tool for advanced logic in Python programming.

📚 Summary and Conclusion

The speaker wraps up the video by summarizing the key points: understanding the basic if-else statement, how to use elif for multiple conditions, using logical operators, and creating nested if statements. They emphasize the flexibility and power of these structures in Python, encouraging viewers to practice writing if-else statements for more complex programming logic. The speaker thanks the audience for watching and encourages them to like and subscribe for more content.

Mindmap

Keywords

💡If Statement

An if statement is a conditional statement in programming that runs a block of code only if a specified condition is true. In the video, it forms the foundation of the decision-making process, where a condition like '25 is greater than 10' is checked to determine if the code block will be executed.

💡Else Statement

An else statement provides an alternative block of code to run if the condition in the if statement evaluates to false. In the video, the else statement is shown when the condition '25 is less than 10' fails, leading the code to print 'it did not work'.

💡Elif Statement

The elif (else if) statement is used to check multiple conditions after the initial if statement. If the first condition fails, the elif condition is checked next. In the video, it is demonstrated as a way to handle several conditions in a chain, such as '25 is less than 30'.

💡Condition

A condition is an expression evaluated by the if, elif, or else statements to determine whether the associated block of code should be executed. For example, in the script, the condition '25 is greater than 10' is evaluated to true, and thus the 'it worked' message is printed.

💡Logical Operator

Logical operators like 'and' and 'or' allow multiple conditions to be combined. In the video, the operator 'or' is used in the statement '25 is less than 10 or 1 is less than 3', which is true because one of the conditions is true, leading to the execution of the block of code.

💡Comparison Operator

Comparison operators compare values, determining if one is greater than, less than, or equal to another. In the video, operators like '>' (greater than) and '<' (less than) are used in examples such as '25 is greater than 10' to compare numbers and make decisions within the code.

💡Indentation

Indentation in Python is used to define the blocks of code that belong to an if, elif, or else statement. The video mentions how Python automatically indents lines following an if statement to signal that the indented lines are part of the conditional block.

💡One-Line If Statement

A one-line if statement allows for writing a conditional statement and the resulting action on a single line. In the video, the instructor demonstrates this by writing 'print it worked if 10 is greater than 30 else print it did not work' to simplify the structure of if-else logic.

💡Nested If Statement

A nested if statement is when an if statement appears inside another if block. This allows for more complex decision-making. In the video, a nested example is used where one if statement checks if '25 is greater than 10', and inside it, another if checks if '10 is greater than 5'.

💡Body of Code

The body of code refers to the indented lines following an if, elif, or else statement that get executed if the condition is true. For instance, in the video, when the condition '25 is greater than 10' is true, the body of code 'print it worked' is executed.

Highlights

Introduction to the if-else statement in Python, explaining its structure and function.

Explanation of the basic if statement: if the condition is true, the code block runs.

Clarification of the elif (else if) statement: checks another condition if the initial if condition is false.

Explanation of the else statement: runs when all previous conditions (if and elif) are false.

Demonstration of a simple if statement: checks if 25 is greater than 10 and prints 'it worked' if true.

Example of an else statement: checks if 25 is less than 10; if false, the else block runs and prints 'it did not work.'

Use of multiple elif conditions: additional elif checks are introduced, demonstrating how they evaluate in sequence.

Illustration of using multiple elif statements: each subsequent elif is evaluated only if all prior conditions are false.

Highlight on the use of logical operators such as 'and' and 'or' within if statements to combine conditions.

Introduction to writing a one-line if-else statement in Python for simpler conditional checks.

Example of a one-line if-else: checks if 10 is greater than 30, prints a result based on the evaluation.

Explanation of nested if statements: placing one if statement inside another to create more complex decision structures.

Demonstration of a nested if statement: checks if 25 is less than 10, and then checks another condition within the first if block.

Emphasis on the flexibility of if-else statements in Python to create highly complex decision-making code.

Final encouragement for understanding if-else logic and nested statements for more advanced Python coding.