Python - convert to string with formatter as parameter

Question

I am trying to write a function which takes two arguments:

an object
a formatter string (as specified in docs)

which then returns a formatted string: What I tried is sort of:

def my_formatter(x, form):
    return str(x).format(form)

What I am expecting is:

s = my_formatter(5, "%2f")
# s = 05
t = my_formatter(5, "%.2")
# t = 5.00

etc...

The format function unfortunately does not work like that. Any ideas?

Martijn Pieters · Accepted Answer · 2014-11-19 13:01:07Z

2

For that style of formatting you'd have to use the string % values string formatting operation:

def my_formatter(x, form):
    return form % x

You'd also have to alter your format; to get 05 you'd have to use "%02d", not "%2f".

You were getting confused by the str.format() method, which uses a different formatting syntax, and you got the arguments swapped; you'd use form.format(x) instead.

You probably want to look into the built-in format() function here; the syntax is slightly different, but offers more features:

>>> format(5, '02d')
'05'
>>> format(5, '.2f')
'5.00'

That's pretty close to what you were already using, minus the %.

edited Nov 19, 2014 at 13:01

answered Nov 19, 2014 at 12:49

Martijn Pieters

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1 Comment

ProfHase85 Over a year ago

Thanks, exactly, I was confused by the str.format method

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