Pythonic way to rewrite the following C++ string processing code - c++

Question

Previous, I am having a C++ string processing code which is able to do this.
input -> Hello 12
output-> Hello
input -> Hello 12 World
output-> Hello World
input -> Hello12 World
output-> Hello World
input -> Hello12World
output-> HelloWorld
The following is the C++ code.
std::string Utils::toStringWithoutNumerical(const std::string& str) {
std::string result;
bool alreadyAppendSpace = false;
for (int i = 0, length = str.length(); i < length; i++) {
const char c = str.at(i);
if (isdigit(c)) {
continue;
}
if (isspace(c)) {
if (false == alreadyAppendSpace) {
result.append(1, c);
alreadyAppendSpace = true;
}
continue;
}
result.append(1, c);
alreadyAppendSpace = false;
}
return trim(result);
}
May I know in Python, what is the Pythonic way for implementing such functionality? Is regular expression able to achieve so?
Thanks.

Answer 1

Edit: This reproduces more accurately what the C++ code does than the previous version.
s = re.sub(r"\d+", "", s)
s = re.sub(r"(\s)\s*", "\1", s)
In particular, if the first whitespace in a run of several whitespaces is a tab, it will preserve the tab.
Further Edit: To replace by a space anyway, this works:
s = re.sub(r"\d+", "", s)
s = re.sub(r"\s+", " ", s)

Answer 2

Python has a lot of built-in functions that can be very powerful when used together.
def RemoveNumeric(str):
return ' '.join(str.translate(None, '0123456789').split())
>>> RemoveNumeric('Hello 12')
'Hello'
>>> RemoveNumeric('Hello 12 World')
'Hello World'
>>> RemoveNumeric('Hello12 World')
'Hello World'
>>> RemoveNumeric('Hello12World')
'HelloWorld'

Answer 3

import re
re.sub(r'[0-9]+', "", string)

Answer 4

import re
re.sub(r"(\s*)\d+(\s*)", lambda m: m.group(1) or m.group(2), string)
Breakdown:
\s* matches zero or more whitespace.
\d+ matches one or more digits.
The parentheses are used to capture the whitespace.
The replacement parameter is normally a string, but it can alternatively be a function which constructs the replacement dynamically.
lambda is used to create an inline function which returns whichever of the two capture groups is non-empty. This preserves a space if there was whitespace and returns an empty string if there wasn't any.

Answer 5

The regular expression answers are clearly the right way to do this. But if you're interested in a way to do if you didn't have a regex engine, here's how:
class filterstate(object):
def __init__(self):
self.seenspace = False
def include(self, c):
isspace = c.isspace()
if (not c.isdigit()) and (not (self.seenspace and isspace)):
self.seenspace = isspace
return True
else:
return False
def toStringWithoutNumerical(s):
fs = filterstate()
return ''.join((c for c in s if fs.include(c)))