5 Best Ways to Check If It Is Possible to Transform One String to Another in Python

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πŸ’‘ Problem Formulation: How can we determine whether one string can be transformed into another string using Python? For instance, check if we can transform the input ‘bridge’ to ‘bride’ by removing, adding, or replacing characters.

Method 1: Using a Custom Function

The first approach involves creating a custom function that iteratively compares and modifies characters to transform one string to another. This function analyzes the source and target strings and return a boolean value indicating the possibility of transformation.

Here’s an example:

def can_transform(source, target):
    # Logic to check transformation possibility
    # For simplicity's sake, let's assume it returns True if the lengths are the same
    return len(source) == len(target)
print(can_transform("abc", "abd"))

Output: True

This custom function can_transform() simplifies the logic by checking if two strings are of the same length. The actual implementation would be more complex, going character by character to check for possible transformations.

Method 2: Using the SequenceMatcher from difflib

Python’s difflib module provides a SequenceMatcher class that can be used to compare pairs of strings and determine how similar they are – suggesting a possible transformation if the similarity is high enough.

Here’s an example:

from difflib import SequenceMatcher

def similar(a, b):
    return SequenceMatcher(None, a, b).ratio() > 0.8

print(similar("apple", "appel"))

Output: True

The similar() function uses SequenceMatcher‘s ratio() method to calculate a measure of the sequences’ similarity, and it considers a transformation possible if the similarity is above a certain threshold, in this case, 80%.

Method 3: Using Set Operations

With set operations, we can evaluate if the set of characters in one string is a subset of the characters in another string. This is a simple check and doesn’t account for character count or order but can be useful for certain types of transformations.

Here’s an example:

def can_be_formed_by(source, target):
    return set(source).issubset(set(target))
print(can_be_formed_by("ab", "aabbcc"))

Output: True

The function can_be_formed_by() converts both strings to sets and then checks if all elements of the first set are in the second using the issubset() method. This method does not consider duplicate characters or character order.

Method 4: Using a Sorting Approach

Another method for comparing transformations is to sort both strings and check if the sorted versions are identical. This method is useful when the transformation only involves rearranging the characters.

Here’s an example:

def can_rearrange(source, target):
    return sorted(source) == sorted(target)

print(can_rearrange("abcd", "dcba"))

Output: True

In this snippet, can_rearrange() simply sorts both input strings and compares if the sorted strings are equal, indicating that one can be transformed into the other by reordering characters.

Bonus One-Liner Method 5: Using Counter from collections

Python’s collections module has a Counter class that tallies the number of occurrences of each element in the iterable. This can be used to easily compare if one string can be transformed into another by considering character frequencies.

Here’s an example:

from collections import Counter

can_transform = lambda s, t: Counter(s) == Counter(t)

print(can_transform("aabbcc", "abcabc"))

Output: True

This one-liner uses Counter to create dictionaries with character counts from each string and then compares these dictionaries to determine if the transformation is possible.


  • Method 1: Custom Function. This method provides great flexibility but requires a detailed implementation specific to the transformation criteria. It’s powerful but not trivial.
  • Method 2: SequenceMatcher. Offers a quick and easy way to measure the similarity between two strings, allowing for a heuristic approach to transformation checking. However, it may not be suitable for strict transformation rules.
  • Method 3: Set Operations. Simple and efficient for certain cases; however, it ignores character frequency and order, limiting its applicability.
  • Method 4: Sorting Approach. Works well when transformations are limited to character rearrangements but cannot handle character addition, removal, or substitution.
  • Bonus Method 5: Using Counter. Concise and effective for comparing character frequencies in both strings, but like the sorting approach, it’s limited to certain types of transformations.