valueerror pattern contains no capture groups

Valueerror: pattern contains no capture groups

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In Python programming, developers often encounter different error messages while working on regular expressions. One of the error messages is the “ValueError: Pattern Contains No Capture Groups“.

This error usually occurs when a regular expression pattern does not consist of any capture groups.

Why does this Valueerror pattern contains no capture groups error occur?

This Valueerror pattern contains no capture groups error occurs when we try to use a regular expression pattern that does not contain any capture groups.

How the Error Reproduce?

This is an example of how the error occurs:

import pandas as pd
example_data = [['Jacob', 'Romeo'],
           ['Rolandita', 'Alvina'],
           ['Kimmy','Kassandra']]
datavalue_sample = pd.DataFrame(data=example_data, columns=['A', 'B'])

result = datavalue_sample['A'].str.extract('Jacob')
print(result)

Output:

Traceback (most recent call last):
File “C:\Users\Dell\PycharmProjects\Python-Code-Example\main.py”, line 7, in
result = datavalue_sample[‘A’].str.extract(‘Joe’)
File “C:\Users\Dell\PycharmProjects\Python-Code-Example\venv\lib\site-packages\pandas\core\strings\accessor.py”, line 129, in wrapper
return func(self, *args, **kwargs)
File “C:\Users\Dell\PycharmProjects\Python-Code-Example\venv\lib\site-packages\pandas\core\strings\accessor.py”, line 2593, in extract
raise ValueError(“pattern contains no capture groups”)
ValueError: pattern contains no capture groups

In the example code above, the error in your code is occurring because the str.extract() method expects a regular expression pattern as an argument, but you’re providing a string literal (‘Jacob’) instead.

Solutions to Fix the ValueError Pattern Contains No Capture Groups

Here are the following solutions to fix the ValueError Pattern Contains No Capture Groups error.

Solution: Used the str.contains() method

To resolve this value error is by using the str.contains() method and extract the rows that consist of the string ‘Jacob’ in column ‘A’.

Here’s an example code:

import pandas as pd

example_data = [['Jacob', 'Romeo'],
           ['Rolandita', 'Alvina'],
           ['Kimmy','Kassandra']]
datavalue_sample = pd.DataFrame(data=example_data, columns=['A', 'B'])

result = datavalue_sample[datavalue_sample['A'].str.contains('Jacob')]
print(result)

Output:

In this updated code, I’ve used the str.contains() method instead of str.extract() to check if the value ‘Jacob’ exists in each row of column ‘A’.

The str.contains() method returns a Boolean Series showing that whether the given pattern is found in each element of the Series.

By using datavalue_sample[‘A’].str.contains(‘Jacob’), we reach a Boolean Series that determine the rows where ‘Jacob‘ is present in column ‘A’.

Finally, we pass this Boolean Series as a filter to the DataFrame datavalue_sample, choosing only the rows that gratify the condition, and assign the result to the variable result. Printing result will give you the desired output.

FAQs

Why am I getting the ValueError: Pattern Contains No Capture Groups error?

The error occurs when the regular expression pattern used does not contain any capture groups.

What are capture groups in regular expressions?

Capture groups in regular expressions are portions of the pattern enclosed within parentheses (). They allow you to extract specific parts of the matched string.

Can I use non-capturing groups instead of capture groups?

Yes, non-capturing groups can be used instead of capture groups when you don’t need to extract the matched substrings separately.

Are capture groups necessary for all regular expressions?

No, capture groups are not necessary for all regular expressions. They are only required when you need to extract specific parts of the matched string.

Conclusion

The Pattern Contains No Capture Groups error is encountered when a regular expression pattern lacks capture groups.

In this article, we discussed an example that triggers this error and provided a solution to resolve it.

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