一个字符串会重复多少次 - python？

Question

I have strings in python like 'abcabcabc', 'abcdbabcdb'. How do I return the number of times a substring repeats itself within a string?

You want to find the longest substring in a string and return the occurrences. The first one would return 3, and the second one would return 2.

Answer 1

Assuming that the repetition of a substring can be partial at the end of the original string (ie the length of the substring is not necessarily an integer divisor of the length of the string), you could do it like this:

def maxRep(s):
 return len(s)/next(i for i in range(1,len(s)+1) if (s[:i]*len(s)).startswith(s))

output:

s = 'abcabcabc'
r = maxRep(s)
print(s,r) # 3.0

s = 'abcdbabcdb'
r = maxRep(s)
print(s,r) # 2.0

s = 'abcdbabcdbab'
r = maxRep(s)
print(s,r) # 2.4

The function uses a brute force approach where every possible length of repeating substring is attempted to see if the result matches the string. The smallest substring length is used (ie the first length that matches) because this will give the greatest number of repetitions.

if you need the substring to be completely repeated (ie no partial substring at the end, you can adjust the function like this:

def maxRep(s):
    return len(s)//next(i for i in range(1,len(s)+1) if not any(s.split(s[:i])))

The condition is based on the fact that splitting the string using the a perfectly repeated substring will only produce empty values in the resulting list

Answer 2

Use regex to find the greatest string that repeat itself:

import re

a = 'abcabcabc'
regex = r'(\w+)(?:.*\1)+'
# greatest must contains: 'abc'
greatest = re.findall(regex, a)[0]

Now you can count the number of occurence:

a.count(greatest)

Answer 3

Do you mean something like this:

def repeat_finder(string):
    for i in range(len(string)//2,0,-1):
        if len(string)%i==0:
            n = len(string)//i
            if string == string[:i]*n:
                return (string[:i],n)
    return 'Not a repeat string.'

repeat_finder('abababab')
repeat_finder('sdlkfkfkfkffdd')
repeat_finder('ababababab')