ProblemYou have a string which you might have read from an external file. The string contains a significant amount of characters that you would like to automatically replace. Show
Possible SolutionsReplacing a single character with another
Here’s the output:
Switch character in string in listIn this example we’ll replace all occurrences of multiple characters from a predefined list by a single character.
Here’s the result:
Replace the first character in a stringIn this example, we’ll go ahead and flip the first character in the string. We can use the count parameter of the string replace() method to ensure that we’ll replace only the first occurrence of that char. Here’s a very simple example:
Here’s the result:
Note that we are able to use the Python code provided in the next section to replace specific positions in the string. For the first character we’ll use the 0 position, and for the last, the -1 position. Replace character at string in a specific positionIn this example, we’ll switch the last character.
Here’s our result: If you’re looking for ways to remove or replace all or part of a string in Python, then this tutorial is for you. You’ll be taking a fictional chat room transcript and sanitizing it using both the In Python, the You’re only given one very short chat transcript:
Even though this transcript is short, it’s typical of the type of chats that agents have all the time. It has user identifiers, ISO time stamps, and messages. In this case, the client The first thing you’ll want to do is to take care of any swear words. How to Remove or Replace a Python String or SubstringThe most basic way to replace a string in Python is to use the >>>
As you can see, you can chain Now it’s time to apply this knowledge to the transcript: >>>
Loading the transcript as a triple-quoted
string and then using the >>>
As you can see, even if the casing of one letter doesn’t match, it’ll prevent any replacements. This means that if you’re using the >>>
Success! But you’re probably thinking that this isn’t the best way to do this for something like a general-purpose transcription sanitizer. You’ll want to move toward some way of having a list of replacements, instead of having to type out Set Up Multiple Replacement RulesThere are a few more replacements that you need to make to the transcript to get it into a format acceptable for independent review:
Now that you’re starting to have more strings to replace, chaining on
In this version of your transcript-cleaning script, you created a list of replacement tuples, which gives you a quick way to add replacements. You could even create this list of tuples from an external CSV file if you had loads of replacements. You then iterate over the list of replacement tuples. In each iteration, you call With this, you’ve made a big improvement in the overall readability of the transcript. It’s also easier to add replacements if you need to. Running this script reveals a much cleaner transcript:
That’s a pretty clean transcript. Maybe that’s all you need. But if your inner automator isn’t happy, maybe it’s because there are still some things that may be bugging you:
If these are your concerns, then you may want to turn your attention to regular expressions. Leverage re.sub() to Make Complex RulesWhenever you’re looking to do any replacing that’s slightly more complex or needs some wildcards, you’ll usually want to turn your attention toward regular expressions, also known as regex. Regex is a sort of mini-language made up of characters that define a pattern. These patterns, or regexes, are typically used to search for strings in find and find and replace operations. Many programming languages support regex, and it’s widely used. Regex will even give you superpowers. In Python, leveraging regex means using the
While you can mix and match the
Now your transcript has been completely sanitized, with all noise removed! How did that happen? That’s the magic of regex. The first regex pattern, Another vital part of the first pattern is that the The second regex pattern uses
character sets and quantifiers to replace the time stamp. You often use character sets and quantifiers together. A regex pattern of There are more quantifiers, though. If you used For the time stamp, you use an extended character set of The time stamp regex pattern allows you to select any possible date in the time stamp format. Seeing as the the times aren’t important for the independent reviewer of these transcripts, you replace them with an empty string. It’s possible to write a more advanced regex that preserves the time information while removing the date. The third regex pattern is used to select any user string that starts with the keyword Finally, the last regex pattern selects the client username string and replaces it with With regex, you can drastically cut down the number of replacements that you have to write out. That said, you still may have to come up with many patterns. Seeing as regex isn’t the most readable of languages, having lots of patterns can quickly become hard to maintain. Thankfully, there’s a neat trick with Use a Callback With re.sub() for Even More ControlOne trick that Python and To get started building this version of the transcript-sanitizing script, you’ll use a basic regex pattern to see how using a callback with
The regex pattern that you’re using will match the time stamps, and
instead of providing a replacement string, you’re passing in a reference to the Since
A match object is one of the building blocks
of the Because you get this match object in the callback, you can use any of the information contained within it to build the replacement string. Once it’s built, you return the new string, and Apply the Callback to the ScriptIn your transcript-sanitizing script, you’ll make use of the
Instead of having lots of different regexes, you can have one top level regex that can match the whole line,
dividing it up into capture groups with brackets (
The content of the capturing groups will be available as separate items in the match object by calling the The two groups are the user string and the
message. The
Note how this architecture allows a very broad and inclusive regex at the top level, and then lets you supplement it with more precise regexes within the replacement callback. The This is now looking like a good first prototype for a transcript-sanitizing script! The output is squeaky clean:
Nice! Using SummaryIn this tutorial, you’ve learned how to replace strings in Python. Along the way, you’ve gone from using the basic Python With all that knowledge, you’ve successfully cleaned a chat transcript, which is now ready for independent review. Not only that, but your transcript-sanitizing script has plenty of room to grow. How do you replace multiple characters in a list Python?We can replace multiple characters in a string using replace() , regex. sub(), translate() or for loop in python.. Character 's' with 'X'.. Character 'a' with 'Y'.. Character 'i' with 'Z'.. How do you replace something in a list Python?We can replace values inside the list using slicing. First, we find the index of variable that we want to replace and store it in variable 'i'. Then, we replace that item with a new value using list slicing.
How do you replace letters in a list?Replace a specific string in a list. If you want to replace the string of elements of a list, use the string method replace() for each element with the list comprehension. If there is no string to be replaced, applying replace() will not change it, so you don't need to select an element with if condition .
How do you replace letters in Python?The Python replace() method is used to find and replace characters in a string. It requires a substring to be passed as an argument; the function finds and replaces it. The replace() method is commonly used in data cleaning.
|