As of now the best way to filter a str is to convert to list, filter, then join back to a str. I think a a string comprehension would be very useful for this.


So to get only ascii_lower case chars given this string,
````
s = "a1b2c3d4"
````

I could do this
````
filtered_s = c"ch for ch in s if ch in string.ascii_lowercase"
````

instead of this.
````
s_list = []
for i in range(len(s)):
    if s[i] in string.ascii_lowercase:
        s_list.append(s[i])

filtered_s = "".join(s_list)
````