python - 在python中提取子字符串

Question

我想解析一个字符串以提取花括号中的所有子字符串:

'The value of x is {x}, and the list is {y} of len {}'

应该产生:

(x, y)

然后我想格式化字符串以打印带有值的初始字符串:

str.format('The value of x is {x}, and the list is {y} of len {}', x, y, len(y))

我该怎么做？

Example usage:
def somefunc():
    x = 123
    y = ['a', 'b']
    MyFormat('The value of x is {x}, and the list is {y} of len {}',len(y))

output:
    The value of x is 123, and the list is ['a', 'b'] of len 2

Answer 1

您可以使用 string.Formatter.parse :

Loop over the format_string and return an iterable of tuples (literal_text, field_name, format_spec, conversion). This is used by vformat() to break the string into either literal text, or replacement fields.

The values in the tuple conceptually represent a span of literal text followed by a single replacement field. If there is no literal text (which can happen if two replacement fields occur consecutively), then literal_text will be a zero-length string. If there is no replacement field, then the values of field_name, format_spec and conversion will be None.

from string import Formatter

s = 'The value of x is {x}, and the list is {y} of len {}'

print([t[1] for t in Formatter().parse(s) if t[1]])
['x', 'y']

不确定这对您尝试做的事情有何帮助，因为您可以在函数中将 x 和 y 传递给 str.format 或使用 **locals:

def somefunc():
    x = 123
    y = ['a', 'b']
    print('The value of x is {x}, and the list is {y} of len {}'.format(len(y),**locals()))

如果你想打印命名参数，你可以添加 Formatter 输出:

def somefunc():
    x = 123
    y = ['a', 'b']
    print("The named args are {}".format( [t[1] for t in Formatter().parse(s) if t[1]]))
    print('The value of x is {x}, and the list is {y} of len {}'.format(len(y), **locals()))

哪个会输出:

The named args are ['x', 'y']
The value of x is 123, and the list is ['a', 'b'] of len 2