将两个.join方法合并为一个

Question

Now I have this :

str = "  s  tr & &^ 23G7/*%45afju657**(%^#%$!!fdf"

str = ''.join(e for e in str if e.isalnum())
str = ''.join(('...', str, '...'))

Can I combine them like :

str = ''.join(('...', e for e in str if e.isalnum(), '...'))

Answer 1

You can use format there

s = "...{}...".format(''.join(e for e in s if e.isalnum()))

As a side note, do not name your string as str as it shadows the builtin

Apart from that, if you really really want to use join twice, you can write it as

''.join(('...', ''.join(e for e in s if e.isalnum()), '...'))

But it is not a good idea. _{Why use a nuclear bomb to kill a mosquito!}

Answer 2

你能做到的

my_str = ''.join(['...']+ [e for e in my_str if e.isalnum()] +['...'])

Answer 3

Why don't you just use the + operator? And filter is also quite nice. Since you use Python 2.7, you don't even need to re-join:

>>> s = "  s  tr & &^ 23G7/*%45afju657**(%^#%$!!fdf"
>>> s = '...' + filter(str.isalnum, s) + '...'
>>> s
'...str23G745afju657fdf...'

Answer 4

string = "  s  tr & &^ 23G7/*%45afju657**(%^#%$!!fdf"

You can use filter() as syntactic sugar for a comprehension. It works best for functions rather than methods, however - the lambda that disguises the string method as a function makes this slow compared to the simple comprehension (thanks, @Bhargav).

string = ''.join(['...', ''.join(filter(lambda x: x.isalnum(), string)), '...'])

or:

string = ''.join(filter(lambda x: x.isalnum(), string)).join(['...']*2)

depending on what ordering you prefer.