python if then assignment

Stack Overflow Public questions & answers
Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers
Talent Build your employer brand
Advertising Reach developers & technologists worldwide
Labs The future of collective knowledge sharing
About the company

Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

If-else conditional assignment in pandas

I want to assign values to a column depending on the values of an already-existing column. This code works, but I would like to do it not-in-place, perhaps using assign or apply .

If this could be done in one step it would also avoid the implicit conversion from int to float that occurs below.

I've included my attempt using assign , which raises a ValueError .

ternary-operator

You can use numpy.where() :

7 original.assign(new=lambda x: np.where(x["col"].isin(["b", "x"]), 1, 99)) is just what I wanted. Thanks. – Hatshepsut Apr 10, 2018 at 21:06

Your Answer

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct .

Not the answer you're looking for? Browse other questions tagged python pandas ternary-operator or ask your own question .

The Overflow Blog
Journey to the cloud part II: Migrating Stack Overflow for Teams to Azure
Computers are learning to decode the language of our minds
Featured on Meta
Sunsetting Winter/Summer Bash: Rationale and Next Steps
Discussions experiment launching on NLP Collective
Temporary policy: Generative AI (e.g., ChatGPT) is banned
Testing an "AI-generated content" policy banner on Stack Overflow

Hot Network Questions

Why are all the neutral wires in a sub panel burnt or melted?
Analogous results in geometric group theory and Riemannian geometry?
How can I transfer my old ship inventory to a new ship inventory?
What is the most common electronics IC package material?
A colorful dodecahedron
Cleaning up a string list
u-substitution shows 0=1
How common is detention pending appeal?
Why is it politically controversial that the President of India referred to herself as the "President of Bharat"?
What's a good way to assert in embedded microcontroller code?
Origin of quote along the lines of "Q: Where do you get your ideas from? A: I get them from Saskatchewan."
Incompatibility of the Lorentz force with electromagnetic radiation
Can an employer exclude you from all meetings during notice period
What would a vehicle with these properties look like? A nomad's caravan
When someone profits from injustice, is life less meaningful?
What would happen if somebody raises someone whose soul has become a demon?
Are there any undecidability results that are not known to have a diagonal argument proof?
Are there downsides to appealing?
Is "may exist" and "may not exist" a negation that isn't a contradiction?
What are some techniques for faster, fine-grained incremental compilation and static analysis?
Infinite upper confidence interval using Fisher exact test in R
Which path to take to Moonrise Towers if I don't want to miss any content?
PVC water pipe used for electical wires to workshop
In the second task of Goblet of Fire, why did Ron make up with Harry?

Your privacy

By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy .

Learn Python practically and Get Certified .

Python Flow Control

Python if...else
Python for Loop

Python while Loop

Python break and continue

Python Pass

Python Functions

Python Function
Function Argument
Python Recursion
Anonymous Function
Global, Local and Nonlocal
Python Global Keyword
Python Modules
Python Package

Python Datatypes

Python Numbers
Python List
Python Tuple
Python String
Python Dictionary

Python Files

Python File Operation
Python Directory
Python Exception
Exception Handling
User-defined Exception

Python Object & Class

Classes & Objects
Python Inheritance
Multiple Inheritance
Operator Overloading

Python Advanced Topics

Python Iterator
Python Generator
Python Closure
Python Decorators
Python Property
Python RegEx
Python Examples

Python Date and time

Python datetime Module
Python datetime.strftime()
Python datetime.strptime()
Current date & time
Get current time
Timestamp to datetime
Python time Module
Python time.sleep()

Python Tutorials

Python pass Statement

Python Assert Statement

Python Exception Handling
Python if...else Statement

In computer programming, we use the if statement to run a block code only when a certain condition is met.

For example, assigning grades (A, B, C) based on marks obtained by a student.

if the percentage is above 90 , assign grade A
if the percentage is above 75 , assign grade B
if the percentage is above 65 , assign grade C

Learn Python with Challenges

Solve challenges and become a Python expert.

In Python, there are three forms of the if...else statement.

if statement
if...else statement
if...elif...else statement

1. Python if statement

The syntax of if statement in Python is:

The if statement evaluates condition .

If condition is evaluated to True , the code inside the body of if is executed.
If condition is evaluated to False , the code inside the body of if is skipped.

Example 1: Python if Statement

In the above example, we have created a variable named number . Notice the test condition,

Here, since number is greater than 0 , the condition evaluates True .

If we change the value of variable to a negative integer. Let's say -5 .

Now, when we run the program, the output will be:

This is because the value of number is less than 0 . Hence, the condition evaluates to False . And, the body of if block is skipped.

2. Python if...else Statement

An if statement can have an optional else clause.

The syntax of if...else statement is:

The if...else statement evaluates the given condition :

If the condition evaluates to True ,

the code inside if is executed
the code inside else is skipped

If the condition evaluates to False ,

the code inside else is executed
the code inside if is skipped

Example 2. Python if...else Statement

Since the value of number is 10 , the test condition evaluates to True . Hence code inside the body of if is executed.

Now if we run the program, the output will be:

Here, the test condition evaluates to False . Hence code inside the body of else is executed.

3. Python if...elif...else Statement

The if...else statement is used to execute a block of code among two alternatives.

However, if we need to make a choice between more than two alternatives, then we use the if...elif...else statement.

The syntax of the if...elif...else statement is:

If condition1 evaluates to true , code block 1 is executed.
If condition2 is true , code block 2 is executed.
If condition2 is false , code block 3 is executed.

Example 3: Python if...elif...else Statement

In the above example, we have created a variable named number with the value 0 . Here, we have two condition expressions:

Here, both the conditions evaluate to False . Hence the statement inside the body of else is executed.

Python Nested if statements

We can also use an if statement inside of an if statement. This is known as a nested if statement.

The syntax of nested if statement is:

We can add else and elif statements to the inner if statement as required.
We can also insert inner if statement inside the outer else or elif statements(if they exist)
We can nest multiple layers of if statements.
Example 4: Python Nested if Statement

In the above example, we have used a nested if statement to check whether the given number is positive, negative, or 0 .

Introduction
Python if statement
Python if...elif...else Statement

Video: Python if...else Statement

Sorry about that.

5 ways to apply an IF condition in Pandas DataFrame

In this guide, you’ll see 5 different ways to apply an IF condition in Pandas DataFrame.

Specifically, you’ll see how to apply an IF condition for:

Set of numbers
Set of numbers and lambda
Strings and lambda
OR condition

Applying an IF condition in Pandas DataFrame

Let’s now review the following 5 cases:

(1) IF condition – Set of numbers

Suppose that you created a DataFrame in Python that has 10 numbers (from 1 to 10). You then want to apply the following IF conditions:

If the number is equal or lower than 4, then assign the value of ‘True’
Otherwise, if the number is greater than 4, then assign the value of ‘False’

This is the general structure that you may use to create the IF condition:

For our example, the Python code would look like this:

Here is the result that you’ll get in Python:

(2) IF condition – set of numbers and lambda

You’ll now see how to get the same results as in case 1 by using lambda, where the conditions are:

Here is the generic structure that you may apply in Python:

And for our example:

This is the result that you’ll get, which matches with case 1:

(3) IF condition – strings

Now, let’s create a DataFrame that contains only strings/text with 4 names : Jon, Bill, Maria and Emma.

The conditions are:

If the name is equal to ‘Bill,’ then assign the value of ‘Match’
Otherwise, if the name is not ‘Bill,’ then assign the value of ‘Mismatch’

Once you run the above Python code, you’ll see:

(4) IF condition – strings and lambda

You’ll get the same results as in case 3 by using lambda:

And here is the output from Python:

(5) IF condition with OR

Now let’s apply these conditions:

If the name is ‘Bill’ or ‘Emma,’ then assign the value of ‘Match’
Otherwise, if the name is neither ‘Bill’ nor ‘Emma,’ then assign the value of ‘Mismatch’

Run the Python code, and you’ll get the following result:

Applying an IF condition under an existing DataFrame column

So far you have seen how to apply an IF condition by creating a new column.

Alternatively, you may store the results under an existing DataFrame column.

For example, let’s say that you created a DataFrame that has 12 numbers, where the last two numbers are zeros:

‘set_of_numbers’: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 , 0 ]

You may then apply the following IF conditions, and then store the results under the existing ‘set_of_numbers’ column:

If the number is equal to 0, then change the value to 999
If the number is equal to 5, then change the value to 555

Here are the before and after results, where the ‘5’ became ‘555’ and the 0’s became ‘999’ under the existing ‘set_of_numbers’ column:

On another instance, you may have a DataFrame that contains NaN values . You can then apply an IF condition to replace those values with zeros , as in the example below:

Before you’ll see the NaN values, and after you’ll see the zero values:

You just saw how to apply an IF condition in Pandas DataFrame . There are indeed multiple ways to apply such a condition in Python. You can achieve the same results by using either lambda, or just by sticking with Pandas.

At the end, it boils down to working with the method that is best suited to your needs.

Finally, you may want to check the following external source for additional information about Pandas DataFrame .

Python If-Else – Python Conditional Syntax Example

In your applications and web projects, there might be times when a user needs to perform an action if a certain condition is met.

There might also be cases when you need to make the user perform another action if the condition is not met.

To do this in Python, you use the if and else keywords. These two keywords are called conditionals.

In this article, I will show you how to implement decision making in your applications with the if and else keywords. I will also show you how the elif keyword works.

I will be using Python comparison operators such as > (greater than), < (less than), and ( == ) equals to compare variables in the if and elif blocks, so we can make the decisions.

How to Use the if Keyword in Python

In Python, the syntax for a single if statement looks like this:

Unlike some other programming languages which use braces to determine a block or scope, Python uses a colon ( : ) and indentation ( 4 whitespaces or a tab ).

So, the indented line or lines of code after the colon will be executed if the condition specified in the braces in front of the if keyword is true.

In the example below, I'm recording the points of 3 soccer teams in 3 variables and making a decision with an if statement.

You can see that the code ran because the condition – teamAPoints > teamBPoints – was met. That is, Team A won the league because they had 99 points as compared to Team B and Team C.

Python has the and keyword that can help us bring Team C into the comparison:

The code ran again because the condition – teamAPoints > teamBPoints and teamCPoints – was met.

If you have only one block of code to execute with the if statement, you can put it in one line and everything would still be okay, as shown below:

This is not a rule, it’s just common practice.

If the condition in the if statement is not met, nothing happens.

By the way, you run Python code in the terminal by typing Python or Python3 followed by the file name, the .py extension, and then hit ENTER on your keyboard. For example, python3 if_else.py .

How to Use the else Keyword in Python

Since nothing happens if the condition in an if statement is not met, you can catch that with an else statement.

With else , you make the user perform an action if the condition in the if statement is not true, or if you want to add more options.

The syntax for if...else is an extension from that of if :

In the code snippet below, the block of code in the else scope runs because the condition specified is not true – Team C doesn’t have more points than Team A.

If you have only one block of code to execute with the if and one with the else , you can put it in one line and everything would still be okay:

Nested if in Python

You can combine what if...else does into a single if statement. This is called nesting in programming languages.

The syntax for nesting 2 or more if statements looks like what you see in the code snippet below:

In nested if , all the conditions must be true for the code to run.

How to Use the elif keyword in Python

Another conditional keyword in Python is elif , which you can put in between an if and else.

In the snippet of code below, you can see how the elif keyword works:

The condition in the if statement did not run because Team A has 99 points

The condition in the elif is true and ran because Team A has 99 points, so the else block was ignored.

In this article, you learned about if…else in Python so you can implement conditionals in your projects.

Thank you for reading, and happy coding.

Web developer and technical writer focusing on frontend technologies. I also dabble in a lot of other technologies.

If you read this far, tweet to the author to show them you care. Tweet a thanks

Learn to code for free. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. Get started

note.nkmk.me

Conditional expression (ternary operator) in python.

Python has a conditional expression (sometimes called a "ternary operator"). You can write operations like if statements in one line with conditional expressions.

6. Expressions - Conditional expressions — Python 3.11.3 documentation

Basics of the conditional expression (ternary operator)

If ... elif ... else ... by conditional expressions, list comprehensions and conditional expressions, lambda expressions and conditional expressions.

See the following article for if statements in Python.

Python if statements (if, elif, else)

In Python, the conditional expression is written as follows.

The condition is evaluated first. If condition is True , X is evaluated and its value is returned, and if condition is False , Y is evaluated and its value is returned.

If you want to switch the value based on a condition, simply use the desired values in the conditional expression.

If you want to switch between operations based on a condition, simply describe each corresponding expression in the conditional expression.

An expression that does not return a value (i.e., an expression that returns None ) is also acceptable in a conditional expression. Depending on the condition, either expression will be evaluated and executed.

The above example is equivalent to the following code written with an if statement.

You can also combine multiple conditions using logical operators such as and or or .

Boolean operators in Python (and, or, not)

By combining conditional expressions, you can write an operation like if ... elif ... else ... in one line.

However, it is difficult to understand, so it may be better not to use it often.

The following two interpretations are possible, but the expression is processed as the first one.

In the sample code below, which includes three expressions, the first expression is interpreted like the second, rather than the third:

By using conditional expressions in list comprehensions, you can apply operations to the elements of the list based on the condition.

See the following article for details on list comprehensions.

List comprehensions in Python

Conditional expressions are also useful when you want to apply an operation similar to an if statement within lambda expressions.

In the example above, the lambda expression is assigned to a variable for convenience, but this is not recommended by PEP8.

Refer to the following article for more details on lambda expressions.

Lambda expressions in Python

Related Categories

How to Write the Python if Statement in one Line

online practice

Have you ever heard of writing a Python if statement in a single line? Here, we explore multiple ways to do exactly that, including using conditional expressions in Python.

The if statement is one of the most fundamental statements in Python. In this article, we learn how to write the Python if in one line.

The if is a key piece in writing Python code. It allows developers to control the flow and logic of their code based on information received at runtime. However, many Python developers do not know they may reduce the length and complexity of their if statements by writing them in a single line.

For this article, we assume you’re somewhat familiar with Python conditions and comparisons. If not, don’t worry! Our Python Basics Course will get you up to speed in no time. This course is included in the Python Basics Track , a full-fledged Python learning track designed for complete beginners.

We start with a recap on how Python if statements work. Then, we explore some examples of how to write if statements in a single line. Let’s get started!

How the if Statement Works in Python

Let’s start with the basics. An if statement in Python is used to determine whether a condition is True or False . This information can then be used to perform specific actions in the code, essentially controlling its logic during execution.

The structure of the basic if statement is as follows:

The <expression> is the code that evaluates to either True or False . If this code evaluates to True, then the code below (represented by <perform_action> ) executes.

Python uses whitespaces to indicate which lines are controlled by the if statement. The if statement controls all indented lines below it. Typically, the indentation is set to four spaces (read this post if you’re having trouble with the indentation ).

As a simple example, the code below prints a message if and only if the current weather is sunny:

The if statement in Python has two optional components: the elif statement, which executes only if the preceding if/elif statements are False ; and the else statement, which executes only if all of the preceding if/elif statements are False. While we may have as many elif statements as we want, we may only have a single else statement at the very end of the code block.

Here’s the basic structure:

Here’s how our previous example looks after adding elif and else statements. Change the value of the weather variable to see a different message printed:

How to Write a Python if in one Line

Writing an if statement in Python (along with the optional elif and else statements) uses a lot of whitespaces. Some people may find it confusing or tiresome to follow each statement and its corresponding indented lines.

To overcome this, there is a trick many Python developers often overlook: write an if statement in a single line !

Though not the standard, Python does allow us to write an if statement and its associated action in the same line. Here’s the basic structure:

As you can see, not much has changed. We simply need to “pull” the indented line <perform_action> up to the right of the colon character ( : ). It’s that simple!

Let’s check it with a real example. The code below works as it did previously despite the if statement being in a single line. Test it out and see for yourself:

Writing a Python if Statement With Multiple Actions in one Line

That’s all well and good, but what if my if statement has multiple actions under its control? When using the standard indentation, we separate different actions in multiple indented lines as the structure below shows:

Can we do this in a single line? The surprising answer is yes! We use semicolons to separate each action in the same line as if placed in different lines.

Here’s how the structure looks:

And an example of this functionality:

Have you noticed how each call to the print() function appears in its own line? This indicates we have successfully executed multiple actions from a single line. Nice!

By the way, interested in learning more about the print() function? We have an article on the ins and outs of the print() function .

Writing a Full Python if/elif/else Block Using Single Lines

You may have seen this coming, but we can even write elif and else statements each in a single line. To do so, we use the same syntax as writing an if statement in a single line.

Here’s the general structure:

Looks simple, right? Depending on the content of your expressions and actions, you may find this structure easier to read and understand compared to the indented blocks.

Here’s our previous example of a full if/elif/else block, rewritten as single lines:

Using Python Conditional Expressions to Write an if/else Block in one Line

There’s still a final trick to writing a Python if in one line. Conditional expressions in Python (also known as Python ternary operators) can run an if/else block in a single line.

A conditional expression is even more compact! Remember it took at least two lines to write a block containing both if and else statements in our last example.

In contrast, here’s how a conditional expression is structured:

The syntax is somewhat harder to follow at first, but the basic idea is that <expression> is a test. If the test evaluates to True , then <value_if_true> is the result. Otherwise, the expression results in <value_if_false> .

As you can see, conditional expressions always evaluate to a single value in the end. They are not complete replacements for an if/elif/else block. In fact, we cannot have elif statements in them at all. However, they’re most helpful when determining a single value depending on a single condition.

Take a look at the code below, which determines the value of is_baby depending on whether or not the age is below five:

This is the exact use case for a conditional expression! Here’s how we rewrite this if/else block in a single line:

Much simpler!

Go Even Further With Python!

We hope you now know many ways to write a Python if in one line. We’ve reached the end of the article, but don’t stop practicing now!

If you do not know where to go next, read this post on how to get beyond the basics in Python . If you’d rather get technical, we have a post on the best code editors and IDEs for Python . Remember to keep improving!

Python if Statement

Summary : in this tutorial, you’ll learn how to use the Python if statement to execute a block of code based on a condition.

The simple Python if statement

You use the if statement to execute a block of code based on a specified condition.

The syntax of the if statement is as follows:

The if statement checks the condition first.

If the condition evaluates to True , it executes the statements in the if-block. Otherwise, it ignores the statements.

Note that the colon ( : ) that follows the condition is very important. If you forget it, you’ll get a syntax error.

The following flowchart illustrates the if statement:

For example:

This example prompts you to input your age. If you enter a number that is greater than or equal to 18 , it’ll show a message "You're eligible to vote" on the screen. Otherwise, it does nothing.

The condition int(age) >= 18 converts the input string to an integer and compares it with 18.

See the following example:

In this example, if you enter a number that is greater than or equal to 18 , you’ll see two messages.

In this example, indentation is very important. Any statement that follows the if statement needs to have four spaces.

If you don’t use the indentation correctly, the program will work differently. For example:

In this example, the final statement always executes regardless of the condition in the if statement. The reason is that it doesn’t belong to the if block:

Python if…else statement

Typically, you want to perform an action when a condition is True and another action when the condition is False .

To do so, you use the if...else statement.

The following shows the syntax of the if...else statement:

In this syntax, the if...else will execute the if-block if the condition evaluates to True . Otherwise, it’ll execute the else-block .

The following flowchart illustrates the if..else statement:

The following example illustrates you how to use the if...else statement:

In this example, if you enter your age with a number less than 18, you’ll see the message "You're not eligible to vote." like this:

Python if…elif…else statement

If you want to check multiple conditions and perform an action accordingly, you can use the if...elif...else statement. The elif stands for else if .

Here is the syntax if the if...elif...else statement:

The if...elif...else statement checks each condition ( if-condition , elif-condition1 , elif-condition2 , …) in the order that they appear in the statement until it finds the one that evaluates to True .

When the if...elif...else statement finds one, it executes the statement that follows the condition and skips testing the remaining conditions.

If no condition evaluates to True , the if...elif...else statement executes the statement in the else branch.

Note that the else block is optional. If you omit it and no condition is True , the statement does nothing.

The following flowchart illustrates the if...elif...else statement:

The following example uses the if...elif..else statement to determine the ticket price based on the age:

In this example:

If the input age is less than 5, the ticket price will be $5.
If the input age is greater than or equal to 5 and less than 16, the ticket price is $10.
Otherwise, the ticket price is $18.
Use the if statement when you want to run a code block based on a condition.
Use the if...else statement when you want to run another code block if the condition is not True .
Use the if...elif...else statement when you want to check multiple conditions and run the corresponding code block that follows the condition that evaluates to True .

Free Python 3 Course
Control Flow
Exception Handling
Python Programs
Python Projects
Python Interview Questions
Python Database
Data Science With Python
Machine Learning with Python
Write an Interview Experience
Share Your Campus Experience
Python – Star or Asterisk operator ( * )
Python 3 – Logical Operators
Python Bitwise Operators
Modulo operator (%) in Python
How To Do Math in Python 3 with Operators?
Difference between “__eq__” VS “is” VS “==” in Python
Python Logical Operators with Examples
Relational Operators in Python
Understanding Boolean Logic in Python 3
Concatenate two strings using Operator Overloading in Python
New ‘=’ Operator in Python3.8 f-string
Python Operators
Operator Overloading in Python
Python Object Comparison : “is” vs “==”
Python Arithmetic Operators
Python | a += b is not always a = a + b
Precedence and Associativity of Operators in Python
Difference between != and is not operator in Python
Python | Operator.countOf
A += B Assignment Riddle in Python
Adding new column to existing DataFrame in Pandas
Python map() function
Read JSON file using Python
How to get column names in Pandas dataframe
Taking input in Python
Read a file line by line in Python
Python Dictionary
Iterate over a list in Python
Enumerate() in Python
Reading and Writing to text files in Python

Assignment Operators in Python

Operators are used to perform operations on values and variables. These are the special symbols that carry out arithmetic, logical, bitwise computations. The value the operator operates on is known as Operand .

Here, we will cover Assignment Operators in Python. So, Assignment Operators are used to assigning values to variables.

Now Let’s see each Assignment Operator one by one.

1) Assign: This operator is used to assign the value of the right side of the expression to the left side operand.

2) Add and Assign: This operator is used to add the right side operand with the left side operand and then assigning the result to the left operand.

Syntax:

3) Subtract and Assign: This operator is used to subtract the right operand from the left operand and then assigning the result to the left operand.

Example –

4) Multiply and Assign: This operator is used to multiply the right operand with the left operand and then assigning the result to the left operand.

5) Divide and Assign: This operator is used to divide the left operand with the right operand and then assigning the result to the left operand.

6) Modulus and Assign: This operator is used to take the modulus using the left and the right operands and then assigning the result to the left operand.

7) Divide (floor) and Assign: This operator is used to divide the left operand with the right operand and then assigning the result(floor) to the left operand.

8) Exponent and Assign: This operator is used to calculate the exponent(raise power) value using operands and then assigning the result to the left operand.

9) Bitwise AND and Assign: This operator is used to perform Bitwise AND on both operands and then assigning the result to the left operand.

10) Bitwise OR and Assign: This operator is used to perform Bitwise OR on the operands and then assigning result to the left operand.

11) Bitwise XOR and Assign: This operator is used to perform Bitwise XOR on the operands and then assigning result to the left operand.

12) Bitwise Right Shift and Assign: This operator is used to perform Bitwise right shift on the operands and then assigning result to the left operand.

13) Bitwise Left Shift and Assign: This operator is used to perform Bitwise left shift on the operands and then assigning result to the left operand.

Please Login to comment...

Improve your coding skills with practice.

Python Tutorial

File handling, python modules, python numpy, python pandas, python matplotlib, python scipy, machine learning, python mysql, python mongodb, python reference, module reference, python how to, python examples, python if else.

The else keyword catches anything which isn't caught by the preceding conditions.

In this example a is greater than b , so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that "a is greater than b".

You can also have an else without the elif :