except as

Learn the exception object with except E as e.

Accessing the object with except ... as

To bind the caught error to a variable you write except ValueError as e:. The e variable holds the error object; you can get the message with str(e) and the type name with type(e).__name__.

This access is needed to show a meaningful message to the user. For example print("Error:", e) prints what the error was. The error object also has properties like .args; this gives the error's parameters as a tuple.

Exercise Bind the error to e and print

In a try block call value = int("abc"). In except ValueError as e: write print("Error:", e). The error message is printed.

Show example solution

# Call int("abc") in a try block
try:
    value = int("abc")
# In except ValueError as e: print the error
except ValueError as e:
    print("Error:", e)

Attributes on e

The error object's e.args attribute gives the error's parameters as a tuple. str(e) joins these into a readable message. type(e).__name__ gives the error class's name.

These attributes are useful when logging errors. For instance with type(e).__name__ you record the error type, with str(e) the message, and with e.args the parameters. This speeds up debugging.

Test yourself

In except ValueError as e, what is e?
- The error type name
- The error object itself
- The line number that raised
- The error message string
Show answer

The error object itself — e is a ValueError instance; str(e) gives its message.
Match the error object attributes

as e

Binds the object to e
str(e)

Error message
type(e).__name__

Type name
e.args

Parameter tuple

Complete the as e clause

except ValueError ____ e:
    print(e)

Show answer

except ValueError as e:
    print(e)

Next lesson: traceback

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