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Python: from first line to project · Lesson 09 / 12
My files and GitHubStudent guide

An error can be a clue

Your program found a word where it expected minutes. Instead of giving up or pretending it worked, let us handle that case.

Learning paths10 min

Let's discover together

  1. 1

    SyntaxError means Python could not parse the structure. ValueError can arise during execution when int receives unsuitable text. Read the type and indicated line; the cause may be earlier.

  2. 2

    try contains the conversion that can fail. except ValueError handles that specific error. Other errors remain visible so unexpected problems are not hidden.

  3. 3

    The example function returns None if conversion fails or the number is not positive. None means no result under this contract; it is not a zero duration.

  4. 4

    Test "15", "abc", "0" and "-2". Do not use except: pass to pretend success. A useful message explains what the user can correct.

✦
YOUR MISSION

Read errors and handle conversion ValueError while keeping failure distinct from success.

Now it's your turn

Discovery workshop

Read, predict, check

Compare the two versions. Show result reveals a prepared output: this panel does not run Python. Then practise with the activity file.
Mini experiment

Learning simulation: compare cards and check your predictions. The browser is not compiling Rust or starting a server.

def parse_minutes(raw):
    try:
        minutes = int(raw)
    except ValueError:
        return None
    if minutes <= 0:
        return None
    return minutes

print(parse_minutes("15"))
Build your answers and check when you are ready.
A moment to understand

Which result distinguishes rejected conversion from a valid duration?

I need a hint

A failure must remain recognisable.

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Take it with you

Run the four suggested inputs. Change the rule to accept only 1 to 180 minutes and add manual tests for 180 and 181.

PYTHON · .py

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