Formatting two numbers in Python

Question

I am coping with the formatting of numbers. I assumed that the .format allows to use multiple arguments:

a = 1.11111111111
b = 0.9
s = '({0:.2f}, {0:.2f})'.format(a, b)
print(s)

Returns:

'(1.11, 1.11)'

Instead of:

'(1.11, 0.90)'

On the other hand, this works fine:

'({}, {})'.format(a, b)

Returns:

'(1.11111111111111, 0.9)'

Any idea where is the problem?

Answer 1

You used for both of the the parameters the value a (0), you should call in the second param to value b (1).

the value before the : is for giving placeholders an explicit positional index.

This allows for re-arranging the order of display without changing the arguments.

Change

s = '({0:.2f}, {0:.2f})'.format(a, b)

To:

s = '({0:.2f}, {1:.2f})'.format(a, b)

Answer 2

Values before the : character specify either a field name or a conversion; by using 0 in both cases you're essentially telling .format, via the element index, to use a in both cases.

In your second case, '({}, {})'.format(a, b), by not specifying a position, .format replaces each empty pair of {} with the elements supplied in increasing order of position.

A simple replacement, as suggested, is to use 1 to indicate that you want to use b instead of a. Alternatively, simply omit them:

s = '({:.2f}, {:.2f})'.format(a, b)

to get a similar effect.

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You should skim through the Syntax for the format strings to get an idea of the rules used when formatting.