Count number strings python

Python String count() Method

The python string count() method is used to count the number of non-overlapping occurrences of the substring that is specified as the function’s parameter.

The count of the substring in a particular range of that string can also be obtained by specifying the start and end of the range in the function’s parameters. The start and end are optional parameters and are interpreted as in slice notation. If the substring is empty, it returns the number of empty strings between the characters which is the length of the string plus one.

In the following section, we will be learning more details about the python string count() method.

Syntax

The syntax of the python string count() method is as follows.

str.count(sub, start= 0,end=len(string))

Parameters

The following are the parameters for the python string count() method.

• sub − This parameter specifies the substring to be searched.
• start − This parameter is an integer value which specifies the starting index from which the search starts. The first character starts from the ‘0’ index. If the start value is not specified, then the default value is ‘0’ that is the first index.
• end − This parameter is an integer value which specifies the ending index at which the search ends. If this value is not specified, then the default search ends at the last index.

Return Value

The python string count() method returns the number of occurrences of the substring from the given input string.

Example

The python string count() method with a substring, start and end values as its parameters returns the count of number of occurrences of the substring within the specified range.

In the following example a string «Hello! Welcome to Tutorialspoint.» is created. Then the substring to be counted is specified as ‘i’. After that, the count() function is invoked on the string with the start value given as 3 and end values as 30 as its arguments.

str = "Hello! Welcome to Tutorialspoint."; substr = "i"; print("The number of occurrences of the substring in the input string are: ", str.count(substr, 3, 30))

On executing the above program, the following output is generated —

The number of occurrences of the substring in the input string are: 2

Example

If the end value is not specified in the function’s parameters, the last index of the string is considered as the default end value.

The following is an example to count the number of occurrences of the substring in the given string with the help of the python string count() function. In this program a string is created and the substring is also specified. Then, the count() function is invoked on the string with the substring and start values as its arguments.

str = "Hello! Welcome to Tutorialspoint."; substr = "to"; print("The number of occurrences of the substring in the input string are: ", str.count(substr, 21))

The following is the output obtained by executing the above program —

The number of occurrences of the substring in the input string are: 0

Example

If the start and end values are not specified in the function’s parameters, the zeroth index of the string is considered as the default start value and the last index of the string is considered as the default end value.

The following is an example to count the number of occurrences of the substring in the given string with the help of the python string count() function.

str = "Hello! Welcome to Tutorialspoint."; substr = "t"; print("The number of occurrences of the substring in the input string are: ", str.count(substr))

The following output is obtained by executing the above program —

The number of occurrences of the substring in the input string are: 3

Example

If the start and end values are not specified in the function’s parameters, the zeroth index of the string is considered as the default start value and the last index of the string is considered as the default end value. If the sub string is empty, it returns the number of empty strings between characters which is the length of the string plus one.

In the following example of the count() function, a string is created and an empty sub string is specified. Then, the count() function is invoked on the string without providing the start and the end values.

str = "Hello! Welcome to Tutorialspoint."; substr = ""; print("The number of occurrences of the substring in the input string are: ", str.count(substr))

The above program, on executing, displays the following output —

The number of occurrences of the substring in the input string are: 34

Example

The substring is a mandatory parameter of the python string count() method. If this parameter is not specified, a type error is occured.

The following is an example to count the number of occurrences of the substring in the input string with the help of the python string count() function. In the following example a string is created. Then, the count() function is invoked on the string with the start and end values as its arguments but the substring to be counted is not specified.

str = "Hello! Welcome to Tutorialspoint."; print("The number of occurrences of the substring in the input string are: ", str.count(2, 21))

The output of the above program is displayed as follows —

Traceback (most recent call last): File "main.py", line 2, in print("The number of occurrences of the substring in the input string are: ", str.count(2, 21)) TypeError: must be str, not int

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Python: Count Number of Occurrences in a String (4 Ways!)

In this post, you’ll learn how to use Python to count the number of occurrences in a string. You’ll learn four different ways to accomplish this, including: the built-in string .count() method and the fantastic counter module.

Knowing how to do this is an incredibly useful skill, allowing you to find, say, duplicate values within a string or deleting unwanted characters (such as special characters).

The Easy Solution: Using String .count()

>>> a_string = 'the quick brown fox jumps over the lazy dog' >>> print(a_string.count('o')) 4

Count Number of Occurrences in a String with .count()

One of the built-in ways in which you can use Python to count the number of occurrences in a string is using the built-in string .count() method. The method takes one argument, either a character or a substring, and returns the number of times that character exists in the string associated with the method.

This method is very simple to implement. In the example below, we’ll load a sample string and then count the number of times both just a character and a substring appear:

>>> a_string = 'the quick brown fox jumps over the lazy dog' >>> print('o appears this many times: ', a_string.count('o')) >>> print('the appears this many times: ', a_string.count('the')) o appears this many times: 4 ui appears this many times: 2

In the example above you used the built-in string .count() method to count the number of times both a single character and a string appeared in a larger string.

Count Number of Occurrences in a Python String with Counter

In order to find a more flexible and efficient way to count occurrences of a character in a Python string, you can also use the Counter object from the built-in collections module. The module provides a number of helpful classes to work with, well, collections of different items.

In this case, our collection will be a string: ‘the quick brown fox jumps over the lazy dog’ .

from collections import Counter a_string = 'the quick brown fox jumps over the lazy dog' collection = Counter(a_string) print(collection) # Returns: Counter()

What we’ve accomplished in the code above is the following:

1. We imported Counter from the collections module
2. We then assigned our string to the variable a_string
3. We passed the string into a Counter object and called it collection
4. Finally, we printed the new collection object

What you can see is that what’s returned is a Counter object. We can confirm this by running print(type(collection)) which returns .

What’s great about this class is that it contains a dictionary-like element that contains occurrences of every iterable item in the item that was passed in.

What this means is that we can access the occurrences of different items in our object by passing in a dictionary accessor.

In the example below, let’s see how we can see how often the letters a and e occur:

>>> print(collection['a']) >>> print(collection['e']) 1 3

This is the magic of the Counter class: it lets you easily access the count of occurrences in Python iterables, such as string.

Use Regular Expressions (Regex) to Count Occurrences in a Python String

You can also use regular expressions (regex) to count the number of occurrences within a Python string. This approach is a little overkill, but if you’re familiar with regex, it can be an easy one to implement!

We’ll use the regular expression module, specifically the .findall() method to load the indices of where the character or substring occurs. Finally, we’ll use Python’s built-in len() function to see how often the character or substring occurs.

>>> import re >>> a_string = 'the quick brown fox jumps over the lazy dog' >>> print(len(re.findall('o', a_string))) 4

We can see that this approach is a bit of an odd way of doing things, especially when compared to the two methods above, covering the built-in .count() method and the built-in Counter class from collections.

Finally, let’s see how we can count occurrences using a for loop.

Use a For Loop to Count Occurrences in a Python String

Using a for loop in Python to count occurrences in a string is a bit of a naive solution, but it can come in handy at times.

The way it works, is that lists are items which you can iterate over (or, often called, iterables), meaning you can loop over each character in a string and count whether a character occurs or not.

Let’s implement the example below and then take a look at how we’ve accomplished everything:

a_string = 'the quick brown fox jumps over the lazy dog' count_o = 0 for character in a_string: if character == 'o': count_o += 1 else: pass print(count_o) # Returns: 4

1. Initialized a new list
2. Set the variable count_o to 0
3. Looped over each character in the string and assessed if it’s equal to o . If it is, we increase the count_o variable by 1. Otherwise, we do nothing.

This solution works, but it’s a bit tedious to write out and it’s not very fast for larger string.

Conclusion

In this post, you learned how to use Python to count occurrences in a string using four different methods. In particular you learned how to count occurrences in a string using the built-in .count() method, the Counter class from collections, the .findall() method from regular expression’s re , as well as how to use a for loop.

If you want to learn more about the Counter class, check out the official documentation here.

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Python String count() Method

Return the number of times the value «apple» appears in the string:

txt = «I love apples, apple are my favorite fruit»

Definition and Usage

The count() method returns the number of times a specified value appears in the string.

Syntax

Parameter Values

Parameter	Description
value	Required. A String. The string to value to search for
start	Optional. An Integer. The position to start the search. Default is 0
end	Optional. An Integer. The position to end the search. Default is the end of the string

More Examples

Example

Search from position 10 to 24:

txt = «I love apples, apple are my favorite fruit»

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