# How to use Python's f-strings with pandas

Python introduced f-strings back in **version 3.6** (six years ago!), but I've only recently realized how useful they can be.

In this post, I'll start by showing you some **simple examples** of how f-strings are used, and then I'll walk you through a **more complex example using pandas**.

Here's what I'll cover:

- Substituting objects
- Calling methods and functions
- Evaluating expressions
- Formatting numbers
- Real-world example using pandas
- Further reading

## Substituting objects:

```
name = 'Kevin'
age = 42
print(f'My name is {name}. I am {age} years old.')
```

`My name is Kevin. I am 42 years old.`

To make an f-string, you simply put an `f`

in front of a string. By putting the `name`

and `age`

objects inside of curly braces, those objects are automatically substituted into the string.

## Calling methods and functions:

```
role = 'Daddy'
print(f'Sometimes my 6-year-old yells: {role.upper()}!!!')
```

`Sometimes my 6-year-old yells: DADDY!!!`

Strings have an `upper()`

method, and so I was able to call that method on the `role`

string from within the f-string.

## Evaluating expressions:

```
days_completed = 37
print(f'This portion of the year remains: {(365 - days_completed) / 365}')
```

`This portion of the year remains: 0.8986301369863013`

You can evaluate an expression (a math expression, in this case) within an f-string.

## Formatting numbers:

`print(f'This percentage of the year remains: {(365 - days_completed) / 365:.1%}')`

`This percentage of the year remains: 89.9%`

This looks much nicer, right? The `:`

begins the format specification, and the `.1%`

means "format as a percentage with 1 digit after the decimal point."

## Real-world example using pandas:

Recently, I was analyzing the survey data submitted by 500+ Data School community members. I asked each person about their **level of experience with 11 different data science topics**, plus their **level of interest** in improving those skills this year.

Thus I had 22 columns of data, with names like:

`python_experience`

`python_interest`

`pandas_experience`

`pandas_interest`

**...**

Each â€śexperienceâ€ť column was coded from **0 (None)** to **3 (Advanced)**, and each â€śinterestâ€ť column was coded from **0 (Not interested)** to **2 (Definitely interested)**.

Among other things, I wanted to know the **mean level of interest in each topic**, as well as the **mean level of interest in each topic by experience level**.

Here's what I did to answer those questions:

```
cats = ['python', 'pandas'] # this actually had 11 categories
for cat in cats:
mean_interest = df[f'{cat}_interest'].mean()
print(f'Mean interest for {cat.upper()} is {mean_interest:.2f}')
print(df.groupby(f'{cat}_experience')[f'{cat}_interest'].mean(), '\n')
```

```
Mean interest for PYTHON is 1.77
python_experience
0 1.590909
1 1.857143
2 1.781759
3 1.630769
Name: python_interest, dtype: float64
Mean interest for PANDAS is 1.67
pandas_experience
0.0 1.500000
1.0 1.825806
2.0 1.709924
3.0 1.262295
Name: pandas_interest, dtype: float64
```

**Notice how I used f-strings:**

- Because of the naming convention, I could access the DataFrame columns using
`df[f'{cat}_interest']`

and`df[f'{cat}_experience']`

. - I capitalized the category using
`f'{cat.upper()}'`

to help it stand out. - I formatted the mean interest to 2 decimal places using
`f'{mean_interest:.2f}'`

.

## Further reading:

- Guide to f-strings (written by my pal Trey Hunner)
- f-string cheat sheet (also by Trey)

**P.S.** This blog post originated as one of my weekly data science tips. Sign up below to receive data science tips every Tuesday! đź‘‡