CODEWITHSUNDEEP
python
Emanuele Paolini
Emanuele Paolini

Reputation: 10162

variable number of digit in format string

Which is a clean way to write this formatting function:

def percent(value,digits=0):
    return ('{0:.%d%%}' % digits).format(value)

>>> percent(0.1565)
'16%'

>>> percent(0.1565,2)
'15.65%'

the problem is formatting a number with a given number of digits, I don't like to use both '%' operator and format method.

Upvotes: 16

Views: 5586

Answers (3)

eumiro
eumiro

Reputation: 212835

I like this one:

'{0:.{1}%}'.format(value, digits)

Test:

>> '{0:.{1}%}'.format(0.1565, 0)
'16%'
>> '{0:.{1}%}'.format(0.1565, 2)
'15.65%'

Upvotes: 38

Chris Morgan
Chris Morgan

Reputation: 90742

* does what you want, for printf-style string formatting.

>>> def percent(value, digits=0):
...     return '%.*f%%' % (digits, value * 100)
...
>>> percent(0.1565, 2)
'15.65%'

Advanced string formatting (defined in PEP 3101 and documented in 7.1.3. Format String Syntax) doesn't seem to be capable of doing this in one pass. (See 7.1.3.1. Format Specification Mini-Language: precision is integer only.)

Upvotes: 3

Inbar Rose
Inbar Rose

Reputation: 43437

From the docs:

Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.

Example:

def percent(value, digits=0):
    print '%.*f%%' % (digits, value*100)
>>> percent(0.1565, 2)
15.65%

Upvotes: 2

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