How to get a string after a specific substring?

Question

How can I get a string after a specific substring?

For example, I want to get the string after "world" in

my_string="hello python world, I'm a beginner"

...which in this case is: ", I'm a beginner")

Answer 1

The easiest way is probably just to split on your target word

my_string="hello python world , i'm a beginner"
print(my_string.split("world",1)[1])

split takes the word (or character) to split on and optionally a limit to the number of splits.

In this example, split on "world" and limit it to only one split.

Answer 2

I'm surprised nobody mentioned partition.

def substring_after(s, delim):
    return s.partition(delim)[2]

s1="hello python world, I'm a beginner"
substring_after(s1, "world")

# ", I'm a beginner"

IMHO, this solution is more readable than @arshajii's. Other than that, I think @arshajii's is the best for being the fastest -- it does not create any unnecessary copies/substrings.

Answer 3

s1 = "hello python world , i'm a beginner"
s2 = "world"

print(s1[s1.index(s2) + len(s2):])

If you want to deal with the case where s2 is not present in s1, then use s1.find(s2) as opposed to index. If the return value of that call is -1, then s2 is not in s1.

Answer 4

You want to use str.partition():

>>> my_string.partition("world")[2]
" , i'm a beginner "

because this option is faster than the alternatives.

Note that this produces an empty string if the delimiter is missing:

>>> my_string.partition("Monty")[2]  # delimiter missing
''

If you want to have the original string, then test if the second value returned from str.partition() is non-empty:

prefix, success, result = my_string.partition(delimiter)
if not success: result = prefix

You could also use str.split() with a limit of 1:

>>> my_string.split("world", 1)[-1]
" , i'm a beginner "
>>> my_string.split("Monty", 1)[-1]  # delimiter missing
"hello python world , i'm a beginner "

However, this option is slower. For a best-case scenario, str.partition() is easily about 15% faster compared to str.split():

                                missing        first         lower         upper          last
      str.partition(...)[2]:  [3.745 usec]  [0.434 usec]  [1.533 usec]  <3.543 usec>  [4.075 usec]
str.partition(...) and test:   3.793 usec    0.445 usec    1.597 usec    3.208 usec    4.170 usec
      str.split(..., 1)[-1]:  <3.817 usec>  <0.518 usec>  <1.632 usec>  [3.191 usec]  <4.173 usec>
            % best vs worst:         1.9%         16.2%          6.1%          9.9%          2.3%

This shows timings per execution with inputs here the delimiter is either missing (worst-case scenario), placed first (best case scenario), or in the lower half, upper half or last position. The fastest time is marked with [...] and <...> marks the worst.

The above table is produced by a comprehensive time trial for all three options, produced below. I ran the tests on Python 3.7.4 on a 2017 model 15" Macbook Pro with 2.9 GHz Intel Core i7 and 16 GB ram.

This script generates random sentences with and without the randomly selected delimiter present, and if present, at different positions in the generated sentence, runs the tests in random order with repeats (producing the fairest results accounting for random OS events taking place during testing), and then prints a table of the results:

import random
from itertools import product
from operator import itemgetter
from pathlib import Path
from timeit import Timer

setup = "from __main__ import sentence as s, delimiter as d"
tests = {
    "str.partition(...)[2]": "r = s.partition(d)[2]",
    "str.partition(...) and test": (
        "prefix, success, result = s.partition(d)\n"
        "if not success: result = prefix"
    ),
    "str.split(..., 1)[-1]": "r = s.split(d, 1)[-1]",
}

placement = "missing first lower upper last".split()
delimiter_count = 3

wordfile = Path("/usr/dict/words")  # Linux
if not wordfile.exists():
    # macos
    wordfile = Path("/usr/share/dict/words")
words = [w.strip() for w in wordfile.open()]

def gen_sentence(delimiter, where="missing", l=1000):
    """Generate a random sentence of length l

    The delimiter is incorporated according to the value of where:

    "missing": no delimiter
    "first":   delimiter is the first word
    "lower":   delimiter is present in the first half
    "upper":   delimiter is present in the second half
    "last":    delimiter is the last word

    """
    possible = [w for w in words if delimiter not in w]
    sentence = random.choices(possible, k=l)
    half = l // 2
    if where == "first":
        # best case, at the start
        sentence[0] = delimiter
    elif where == "lower":
        # lower half
        sentence[random.randrange(1, half)] = delimiter
    elif where == "upper":
        sentence[random.randrange(half, l)] = delimiter
    elif where == "last":
        sentence[-1] = delimiter
    # else: worst case, no delimiter

    return " ".join(sentence)

delimiters = random.choices(words, k=delimiter_count)
timings = {}
sentences = [
    # where, delimiter, sentence
    (w, d, gen_sentence(d, w)) for d, w in product(delimiters, placement)
]
test_mix = [
    # label, test, where, delimiter sentence
    (*t, *s) for t, s in product(tests.items(), sentences)
]
random.shuffle(test_mix)

for i, (label, test, where, delimiter, sentence) in enumerate(test_mix, 1):
    print(f"\rRunning timed tests, {i:2d}/{len(test_mix)}", end="")
    t = Timer(test, setup)
    number, _ = t.autorange()
    results = t.repeat(5, number)
    # best time for this specific random sentence and placement
    timings.setdefault(
        label, {}
    ).setdefault(
        where, []
    ).append(min(dt / number for dt in results))

print()

scales = [(1.0, 'sec'), (0.001, 'msec'), (1e-06, 'usec'), (1e-09, 'nsec')]
width = max(map(len, timings))
rows = []
bestrow = dict.fromkeys(placement, (float("inf"), None))
worstrow = dict.fromkeys(placement, (float("-inf"), None))

for row, label in enumerate(tests):
    columns = []
    worst = float("-inf")
    for p in placement:
        timing = min(timings[label][p])
        if timing < bestrow[p][0]:
            bestrow[p] = (timing, row)
        if timing > worstrow[p][0]:
            worstrow[p] = (timing, row)
        worst = max(timing, worst)
        columns.append(timing)

    scale, unit = next((s, u) for s, u in scales if worst >= s)
    rows.append(
        [f"{label:>{width}}:", *(f" {c / scale:.3f} {unit} " for c in columns)]
    )

colwidth = max(len(c) for r in rows for c in r[1:])
print(' ' * (width + 1), *(p.center(colwidth) for p in placement), sep="  ")
for r, row in enumerate(rows):
    for c, p in enumerate(placement, 1):
        if bestrow[p][1] == r:
            row[c] = f"[{row[c][1:-1]}]"
        elif worstrow[p][1] == r:
            row[c] = f"<{row[c][1:-1]}>"
    print(*row, sep="  ")

percentages = []
for p in placement:
    best, worst = bestrow[p][0], worstrow[p][0]
    ratio = ((worst - best) / worst)
    percentages.append(f"{ratio:{colwidth - 1}.1%} ")

print("% best vs worst:".rjust(width + 1), *percentages, sep="  ")

Answer 5

If you want to do this using regex, you could simply use a non-capturing group, to get the word "world" and then grab everything after, like so

(?:world).*

The example string is tested here

Answer 6

In Python 3.9, a new removeprefix method is being added:

>>> 'TestHook'.removeprefix('Test')
'Hook'
>>> 'BaseTestCase'.removeprefix('Test')
'BaseTestCase'

• Documentation: https://docs.python.org/3.9/library/stdtypes.html#str.removeprefix
• Announcement: https://docs.python.org/3.9/whatsnew/3.9.html

Answer 7

You can use the package called substring. Just install using the command pip install substring. You can get the substring by just mentioning the start and end characters/indices.

For example:

import substring
s = substring.substringByChar("abcdefghijklmnop", startChar="d", endChar="n")
print(s)

Output:

# s = defghijklmn

Answer 8

Try this general approach:

import re

my_string="hello python world , i'm a beginner"
p = re.compile("world(.*)")
print(p.findall(my_string))

# [" , i'm a beginner "]

Answer 9

It's an old question but i faced a very same scenario, i need to split a string using as demiliter the word "low" the problem for me was that i have in the same string the word below and lower.

I solved it using the re module this way

import re

string = '...below...as higher prices mean lower demand to be expected. Generally, a high reading is seen as negative (or bearish), while a low reading is seen as positive (or bullish) for the Korean Won.'

# use re.split with regex to match the exact word
stringafterword = re.split('\\blow\\b',string)[-1]

print(stringafterword)
# ' reading is seen as positive (or bullish) for the Korean Won.'

# the generic code is:
re.split('\\bTHE_WORD_YOU_WANT\\b',string)[-1]

Hope this can help someone!

Answer 10

If you prefer to do it using only python regular expressions re library, you can do it with Match.string property and Match.end() method of the Match object:

import re

my_string="hello python world, I'm a beginner"

match = re.search("world", my_string)

if match:
    print(match.string[match.end():])
    # , I'm a beginner