What is a function?

Introduction to Data Science in Python

Hillary Green-Lerman

Lead Data Scientist, Looker

A function is an action

function-analogy

Functions in code

import pandas as pd
from matplotlib import pyplot as plt

df = pd.read_csv('letter_frequency.csv')

plt.plot(df.letter_index, df.frequency, label='Ransom')
plt.show()

Functions perform actions:

pd.read_csv() turns a csv file into a table in Python
plt.plot() turns data into a line plot
plt.show() displays plot in a new window

Anatomy of a function: function name

function-anatomy

Function Name:

Starts with the module that the function "lives" in (plt)
Followed by the name of the function (plot)
Function name is always followed by parentheses ()

Anatomy of a function: positional arguments

function-anatomy

Positional Arguments:

These are inputs to a function; they tell the function how to do its job
Order matters!

Anatomy of a function: keyword arguments

function-anatomy

Keyword Arguments:

Must come after positional arguments
Start with the name of the argument (label), then an equals sign (=)
Followed by the argument (Ransom)

Common function errors

Missing commas between arguments

Missing closed parenthesis

Let's practice!

Introduction to Data Science in Python