如何修复KeyError：'w'。 在python中进行字符串格式化时得到了它

Question

I am trying to print the decimal, octal, hex and binary representation of a given number with format :

number = int(input())
w = len('{0:b}'.format(number))
print("{0:{w}d} {0:{w}o} {0:{w}X} {0:{w}b}".format(number))

The format that I am expecting is as below (say for input 17):

17    21    11 10001

Answer 1

You need to use the format_spec keyword arguments for format(value[, format_spec]) :

>>> print("{text}".format(text="hello"))

Therefore in your case:

>>> number = 17
>>> w = len('{0:b}'.format(number))
>>> print("{0:{w}d} {0:{w}o} {0:{w}X} {0:{w}b}".format(number, w=w))

if you want number variable to be replaced in the {0} placeholder and w variable in {w} placeholder.

You can find a very similar example in the Format examples in the documentation if you search for "nesting":

Nesting arguments and more complex examples:

>>> for align, text in zip('<^>', ['left', 'center', 'right']):
...     '{0:{fill}{align}16}'.format(text, fill=align, align=align)
...
'left<<<<<<<<<<<<'
'^^^^^center^^^^^'
'>>>>>>>>>>>right'