22 Pythonic Tricks for Working with Strings

String manipulation is something we Pythonistas do a lot. Here are 20 top tips & tricks you might find useful!

All these examples are using Python 3, at the time of writing the latest version is 3.8.2. If you’re new to programming, you’ll find my Introduction to Strings article useful.

0. Is a Substring in a String?

Use the in-built comparator in which returns True or False

1. Reverse a String

Use a slice with a decreasing step to return the reversed string.

2. Compare Two Strings for Equality

Compare equality using == to see if two objects have an equal value.
Compare identity using is to see if two objects are one and the same.

3. Lowercase, Uppercase, Sentence Case and Title Case of a String

Python has a number of in-built functions you can use to change the case of a string.

4. Concatenate Strings Efficiently

Use join on an empty string to concatenate the parameters.
This function receives a variable number of arguments using the special * indicator.

5. Is the String Empty or None?

A perfectly fine string object can contain 0 characters, or all whitespace, or even be the None object. 
This function can be used if you want to test for character or byte content in the string.

6. Trim Leading and Trailing Whitespace

The following function returns a 3-tuple, each element contains a version of the original string but stripped of whitespace in a different way in each.
On line 6 you can see that Python understands statements which assign values to multiple variables.

7. Generate a String of Random Characters

Use the secrets module to make random choices of characters to add to a string.

8. Read the Lines in a File to a List

The file reader object f is being converted to a list implicitly here.
Note: here we’re open the file in ‘r’ mode for read-only.

9. Tokenize a Sentence Fully

Tokenization is a procedure in natural language processing — it returns all tokens in a sentence including punctuation. We’ll use NLTK, which you’ll need to install separately.

10. Execute Python Code Found Inside a String

Here there are two methods being displayed. exec_string will send the contents of a string to the operating system. eval_string will use Python to evaluate the string.

Be careful with both, the strings you are executing might be malicious!

11. Find the Substring Between Two Markers

Use regular expressions and F-Strings.

12. Remove all Punctuation from a String

The strings module contains a list of punctuation characters.
Use translate (see #21) to remove them from the string.

13. Encode and Decode UTF-8 URLs

UTF-8 allows us to use extended, double-word characters — such as emojis. These need to be encoded before they can be used in a URL.

14. Use Base64 Encoding on Strings

Base64 is a method to encode binary data as a string for transmitting in text messages. You can also use it to encode UTF-8 strings.

15. Calculate the Similarity of Two Strings

Aside from using the Levenshtein distance in nltk.edit_distance, you could try the difflib library.
A value of 1.0 would indicate equality.

16. Remove a Character at a Specific Index

Again, strings are a sequence of characters, so you can use slicing operations.

17. Convert Between CSV and List

Comma-separated values are everywhere because Excel is the best, general-purpose solution to any data problem! ;)
Let’s take a single of CSV line and convert it into a list of values.

Line 3 composes a list, splitting the input line on every “,” separator.

Now let’s do the reverse: take a list and return a CSV line.

18. Weave Two Strings

Use zip_longest from the itertools module to zip two strings of unequal length.
This solution joins the output a list comprehension which concatenates i + j.

19. Remove Unwanted Characters from a String

Use the replace function. Remember: you can’t change the value of a string in-place — strings are immutable.
Also, see #21.

20. Find the Index Locations of a Character in a String

This solution uses a list comprehension with a filter using if.

21. Translate a String to Leetspeak

Use the functions maketrans and translate.

Have fun Pythonistas!