Introduction to errors

Intermediate Python for Developers

George Boorman

Curriculum Manager, DataCamp

What is an error?

Code that violates one or more rules
Error = Exception
Cause our code to terminate!

Hierarchy of some Python exceptions

¹ https://docs.python.org/3/library/exceptions.html#exception-hierarchy

TypeError

Incorrect data type

"Hello" + 5

TypeError output showing strings and integers cannot be combined

ValueError

float("Hello")

ValueError output confirming that the string 'Hello' cannot be converred to a float

The value is not acceptable in an acceptable range

float("2")

Output showing the result 2.0 without an error

Tracebacks

Traceback message

Tracebacks

Traceback message highlighting the error type

Tracebacks

Traceback message highlight the code that caused the error

Code in packages

Packages contain other people's code e.g., custom functions
Known as source code
pip install <package> downloads source code to our local environment
The pandas' pd.read_csv() function executes the code written for that custom function behind the scenes

Tracebacks from packages

# Import pandas package
import pandas as pd

# Create pandas DataFrame                 
products = pd.DataFrame({"ID": "ABC1",
                         "price": 29.99})

# Try to access the non-existent "tag" column
products["tag"]

Tracebacks from packages

Traceback from trying to subset a pandas DataFrame on a non-existent column

Tracebacks from packages

Traceback showing the file that produced an error when executed, along with the error type of KeyError

Tracebacks from packages

Traceback showing the line in our code that caused the error

Tracebacks from packages

Traceback showing code that intentionally returns an error

Let's practice!

Intermediate Python for Developers