Count the number of times a particular string appears in a given word

Question

How to write a program that prints the number of times a particular string appears in a given word. For example: if I'm looking for the string 'dad' in a word 'asdadgfrdad' output should be 2.

def numStrings(a):
    strings = 'dad'
    result = 0
    for char in a:
        if char in strings:
            result = result + 1
    print result

numStrings("asdadgfrdad")

But this gives me the number of times the letters d,a are present in the given word. How to correct this?

Strings have a builtin method for that: docs.python.org/2/library/stdtypes.html#str.count — BrenBarn
– BrenBarn, Commented Jun 21, 2015 at 19:39
Do you need overlapping strings? eg: What's the correct count for "dadadad"? — Jon Clements
– Jon Clements, Commented Jun 21, 2015 at 19:43
Another tip: the pythonic naming convention is snake_case instead of camelCase. — Mehdi
– Mehdi, Commented Jun 21, 2015 at 19:47

Jay Bosamiya · Accepted Answer · 2015-06-21 19:53:19Z

9

The short and simple pythonic way to do it would be

'asdadgfrdad'.count('dad')

However, your answer may or may not be what you expect when you look at something like 'dadad'.count('dad') which returns 1 instead of 2. This is because str.count returns the number of non-overlapping occurrences of substring. On the other hand, if you want to find the number of overlapping substrings, you'll have to use the following code:

haystack = 'dadad'
needle = 'dad'
sum(haystack[i:i+len(needle)] == needle for i in range(len(haystack)))

edited Jun 21, 2015 at 19:53

answered Jun 21, 2015 at 19:40

Jay Bosamiya

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2 Comments

coder123 Over a year ago

Can u please tell me where to use the last code? i tried including it in my code but i'm not getting the desired output.

Jay Bosamiya Over a year ago

You'll have to use the last line as an expression, for example num_repeats = sum(haystack[i:i+len(needle)] == needle for i in range(len(haystack))) and then use num_repeats variable as you would like. (such as printing it etc)

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