Lessons · Python · text vs numbers

Text that looks like a number is still text

"5" and 5 are different things. Convert at the boundary with int() or float(), and never do arithmetic on the text.

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What it is for

Form fields, CSV cells, query strings, environment variables all arrive as text. '1' + '2' being '12' is the bug that follows.

Ask: where did this value come from? If from outside the program, convert it once as it enters, then treat it as a number everywhere else.

age_text = input()  # user typed 34

Text, always.

age = int(age_text)

Now a number.

print(age + 1)

35. With the text version you would get an error, or '341'.

Read a price from a CSV cell.

price = (cell)

int("3.5") fails; use float. And int(" 3 ") works, but int("3 apples") does not; validate before converting.

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