Python Get the numeric prefix of given string

Sometimes we need to extract the numeric prefix from a string that contains numbers at the beginning. Python provides several approaches to extract only the numeric part from the start of a string.

Using takewhile() with isdigit()

The isdigit() method checks if each character is a digit. Combined with takewhile() from itertools, we can extract consecutive digits from the beginning ?

from itertools import takewhile

# Given string
string_data = "347Hello"
print("Given string:", string_data)

# Using takewhile with isdigit
result = ''.join(takewhile(str.isdigit, string_data))

print("Numeric prefix from the string:", result)

The output of the above code is ?

Given string: 347Hello
Numeric prefix from the string: 347

Using re.sub() Pattern Replacement

Regular expressions can remove non-digit characters after the initial numeric sequence. The pattern \D.* matches any non-digit followed by any characters ?

import re

# Given string
string_data = "347Hello"
print("Given string:", string_data)

# Using re.sub to remove non-digits after initial digits
result = re.sub(r'\D.*', '', string_data)

print("Numeric prefix from the string:", result)

The output of the above code is ?

Given string: 347Hello
Numeric prefix from the string: 347

Using re.match() for Exact Prefix

The match() function specifically looks for patterns at the beginning of a string, making it ideal for extracting numeric prefixes ?

import re

# Given string
string_data = "347Hello"
print("Given string:", string_data)

# Using re.match to find digits at start
match = re.match(r'\d+', string_data)
result = match.group() if match else ''

print("Numeric prefix from the string:", result)

The output of the above code is ?

Given string: 347Hello
Numeric prefix from the string: 347

Comparison of Methods

Conclusion

Use takewhile() for simple digit extraction without regex complexity. Use re.match() when you specifically want to match patterns at the string beginning.