Python check if string contains only letters

By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Return true if all characters in the string are alphabetic and there is at least one character, false otherwise. For people finding this question via Google who might want to know if a string contains only a subset of all letters, I recommend using regexes:.

More generally, all returns True if the objects in your iterable would be considered True. These would be considered False. Actually, we're now in globalized world of 21st century and people no longer communicate using ASCII only so when anwering question about "is it letters only" you need to take into account letters from non-ASCII alphabets as well.

Python has a pretty cool unicodedata library which among other things allows categorization of Unicode characters:. The categories and their abbreviations are defined in the Unicode standard.

From here you can quite easily you can come up with a function like this:. As you can see the whitelisted categories can be quite easily controlled by the tuple inside the function. See this article for a more detailed discussion. The match method will return a Match object if a match is found. Otherwise it will return None.

Learn more. How can I check if a string only contains letters in Python? Ask Question. Asked 6 years, 7 months ago. Active 8 months ago. Viewed k times. I'm trying to check if a string only contains letters, not digits or symbols.

Martin Thoma Given a string, write a Python program to find whether a string contains only letters and no other keywords. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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python check if string contains only letters

Writing code in comment? Please use ide. Python code to demonstrate. Code to check whther string contains only number. Recommended Posts: Python Ways to check string contain all same characters Python Ways to split a string in different ways Reverse string in Python 5 different ways Python Ways to check if element exists in list Python Ways to concatenate boolean to string Find length of a string in python 4 ways Python Ways to find all permutation of a string Ways to remove i'th character from string in Python Python Ways to convert string to json object Python Ways to remove numeric digits from given string Python Ways to sort letters of string alphabetically Python Ways to remove n characters from start of given string Python Ways to count number of substring in string Python Ways to find nth occurrence of substring in a string Python Ways to convert list of ASCII value to string.

Check out this Author's contributed articles. Load Comments.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I know how to do this if I iterate through all of the characters in the string but I am looking for a more elegant method.

Use string. This is pretty fast as it uses the underlying C function to do the work, with very little python bytecode involved. Obviously performance isn't everything - going for the most readable solutions is probably the best approach when not in a performance critical codepath, but just to see how the solutions stack up, here's a performance comparison of all the methods proposed so far. The set approaches are usually worst, beating regexes only for the empty string case.

There's a similar difference between the regex methods matching all valid characters and searching for invalid characters. Matching performs a little better when checking for a long, but fully valid string, but worse for invalid characters near the end of the string. There are a variety of ways of achieving this goal, some are clearer than others. For each of my examples, 'True' means that the string passed is valid, 'False' means it contains invalid characters.

Then there's use of a regular expression, you can do this with re. Note that '-' has to be at the end of the [] otherwise it will be used as a 'range' delimiter. Another solution noted that you can do an inverse match with regular expressions, I've included that here now.

How to check if a string has at least one letter and one number in Python?

You can also do something tricky with the 'set' object. Have a look at this example, which removes from the original string all the characters that are allowed, leaving us with a set containing either a nothing, or b the offending characters from the string:. Section 3. I guess you don't accept blank input. You need these two special characters since you need to avoid the following case. You could always use a list comprehension and check the results with all, it would be a little less resource intensive than using a regex: all [c in string.

Which, to quote Joel Spolsky, is something of a Shlemiel the Painter algorithm. But testing for existence in a set should be more efficient, or at least less dependent on the number of allowed characters. Certainly this approach is a little bit faster on my machine. It's clear and I think it performs plenty well enough for most cases on my slow machine I can validate tens of thousands of short-ish strings in a fraction of a second. I like it. So that probably is the best way forward.

Learn more. How do I verify that a string only contains letters, numbers, underscores and dashes? Ask Question. Asked 11 years, 6 months ago. Active 11 months ago. Viewed k times.One of the most common operations that programmers use on strings is to check whether a string contains some other string. If you are coming to Python from Java, for instance, you might have used the contains method to check if some substring exists in another string.

How to check if a string has at least one letter and one number in Python?

Unlike the in operator which is evaluated to a boolean value, the find method returns an integer. This integer is essentially the index of the beginning of the substring if the substring exists, otherwise -1 is returned.

One cool thing about this method is you can optionally specify a start index and an end index to limit your search within. Assume for a second that Python has no built-in functions or methods that would check if a string contains another string.

Well, an easy way is to brute force by checking if the substring exists starting from every possible position in the original string. I highly recommend this article from TopCoder if you want to learn more and dive deeper into string searching algorithms. For more coverage of other string searching algorithms not covered in the previous article, this wikipedia page is great. It is very clear now that the find method uses a mix of boyer-moore and horspool algorithms.

The in operator returns True if the substring exists in the string. Otherwise, it returns False. The find method returns the index of the beginning of the substring if found, otherwise -1 is returned.

Pretty explanatory and it helped me with some question I had!

python check if string contains only letters

Found a mistake in this article though. Thanks Guilherme. View Larger Image. In Python, there are two ways to achieve this. Otherwise, it returns false. This method is very straightforward, clean, readable, and idiomatic. Some Advanced Stuff Assume for a second that Python has no built-in functions or methods that would check if a string contains another string. How would you write a function to do that? For larger strings, this process can be really slow.

Python | Ways to check if given string contains only letter

There are better algorithms for string searching. Learning Python? No longer a beginner? Are you Beginning your Programming Career? I provide my best content for beginners in the newsletter. What programming language to start with? Do you need a CS degree to be a programmer? Career tips and advice Programming tutorials And so much moreā€¦ Subscribe now. This comment form is under antispam protection.

Most reacted comment. Hottest comment thread. Notify of. But you should correct the mistake cited by him.In this article, we'll examine four ways to use Python to check whether a string contains a substring. The easiest way to check if a Python string contains a substring is to use the in operator. The in operator is used to check data structures for membership in Python. It returns a Boolean either True or False and can be used as follows:. The String type in Python has a method called index that can be used to find the starting index of the first occurrence of a substring in a string.

If the substring is not found, a ValueError exception is thrown, which can to be handled with a try-except-else block:. This method is useful if you need to know the position of the substring, as opposed to just its existence within the full string. The String type has another method called find which is more convenient to use than indexbecause we don't need to worry about handling any exceptions.

If find doesn't find a match, it returns -1, otherwise it returns the left-most index of the substring in the larger string. If you'd prefer to avoid the need to catch errors, then this method should be favored over index. Regular expressions provide a more flexible albeit more complex way to check strings for pattern matching. Python is shipped with a built-in module for regular expressions, called re. The re module contains a function called searchwhich we can use to match a substring pattern as follows:.

This method is best if you are needing a more complex matching function, like case insensitive matching. Otherwise the complication and slower speed of regex should be avoided for simple substring matching use-cases. This article was written by Jacob Stopak, a software consultant and developer with passion for helping others improve their lives through code.

python check if string contains only letters

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Subscribe to our Newsletter Get occassional tutorials, guides, and jobs in your inbox. Newsletter Signup.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I could iterate over each character and check the character is a. Note: There is a comparison with using re. Further timings show that match would win with much longer strings; match seems to have a much larger overhead than search when the final answer is True; this is puzzling perhaps it's the cost of returning a MatchObject instead of None and may warrant further rummaging.

Here's a simple, pure-Python implementation. It should be used when performance is not critical included for future Googlers. Regarding performance, iteration will probably be the fastest method. Regexes have to iterate through a state machine, and the set equality solution has to build a temporary set. However, the difference is unlikely to matter much. If performance of this function is very important, write it as a C extension module with a switch statement which will be compiled to a jump table.

Here's a C implementation, which uses if statements due to space constraints. If you absolutely need the tiny bit of extra speed, write out the switch-case.

In my tests, it performs very well 2 seconds vs 9 seconds in benchmarks against the regex. Under request I'm going to return the other part of the answer. But please note that the following accept A-Z range. You can use isalnum. EDIT2 John gave an example where the above doesn't work. I changed the solution to overcome this special case by using encode. This has already been answered satisfactorily, but for people coming across this after the fact, I have done some profiling of several different methods of accomplishing this.

In my case I wanted uppercase hex digits, so modify as necessary to suit your needs. The columns we actually care about are cumtime and percall, as that shows us the actual time taken from function entry to exit. As we can see, regex match and search are not massively different. It is faster not to bother compiling the regex if you would have compiled it every time. It is about 7. Use python Sets when you need to compare hm Strings can be represented as sets of characters quite fast.

python check if string contains only letters

Here I test if string is allowed phone number. First string is allowed, second not.Given a string, write a Python program to find whether a string contains only letters and no other keywords. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below. Writing code in comment?

Please use ide. Python code to demonstrate. Code to check whther string contains only number. Recommended Posts: Python Ways to check string contain all same characters Python Ways to split a string in different ways Reverse string in Python 5 different ways Python Ways to check if element exists in list Python Ways to concatenate boolean to string Ways to remove i'th character from string in Python Python Ways to find all permutation of a string Find length of a string in python 4 ways Python Ways to sort letters of string alphabetically Python Ways to find nth occurrence of substring in a string Python Ways to remove n characters from start of given string Python Ways to remove numeric digits from given string Python Ways to convert string to json object Python Ways to count number of substring in string Python Ways to convert list of ASCII value to string.

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