从python字符串中提取子字符串

Question

I want to extract the string before the 9 digit number below:

tmp = place1_128017000_gw_cl_mask.tif

The output should be place1

I could do this: tmp.split('_')[0] but I also want the solution to work for:

tmp = place1_place2_128017000_gw_cl_mask.tif where the result would be: place1_place2

You can assume that the number will also be 9 digits long

Answer 1

Assuming we can phrase your problem as wanting the substring up to, but not including the underscore which is followed by all numbers, we can try:

tmp = "place1_place2_128017000_gw_cl_mask.tif"
m = re.search(r'^([^_]+(?:_[^_]+)*)_\d+_', tmp)
print(m.group(1))  # place1_place2

Answer 2

Using regular expressions and the lookahead feature of regex, this is a simple solution:

tmp = "place1_place2_128017000_gw_cl_mask.tif"
m = re.search(r'.+(?=_\d{9}_)', tmp)
print(m.group())

Result:

place1_place2

Note that the \d{9} bit matches exactly 9 digits. And the bit of the regex that is in (?= ... ) is a lookahead, which means it is not part of the actual match, but it only matches if that follows the match.

Answer 3

Use a regular expression:

import re

places = (
    "place1_128017000_gw_cl_mask.tif",
    "place1_place2_128017000_gw_cl_mask.tif",
)
pattern = re.compile("(place\d+(?:_place\d+)*)_\d{9}")
for p in places:
    matched = pattern.match(p)
    if matched:
        print(matched.group(1))

prints:

place1

place1_place2

The regex works like this (adjust as needed, eg, for less than 9 digits or a variable number of digits):

• ( starts a capture
• place\d+ matches "places plus 1 to many digits"
• (?: starts a group, but does not capture it (no need to capture)
• _place\d+ matches more "places"
• ) closes the group
• * means zero or many times the previous group
• ) closes the capture
• \d{9} matches 9 digits

The result is in the first (and only) capture group.

Answer 4

Here's a possible solution without regex (unoptimized!):

def extract(s):
    result = ''
    for x in s.split('_'):
        try: x = int(x)
        except: pass
        if isinstance(x, int) and len(str(x)) == 9:
            return result[:-1]
        else:
            result += x + '_'

tmp = 'place1_128017000_gw_cl_mask.tif'
tmp2 = 'place1_place2_128017000_gw_cl_mask.tif'

print(extract(tmp))   # place1
print(extract(tmp2))  # place1_place2