4 Answers. Asking for help, clarification, or responding to other answers. If each character is either an alphabet or a number, then true is returned from the function or else false will be returned. If I check for each character ,most of them would return false. Here is the program to Does disabling TLS server certificate verification (E.g. WebThat won't quite work: String.matches () in Java checks if the regex matches the whole string. Why can a transistor be considered to be made up of diodes? How do I check if an object has an attribute? I'm an absolute beginner trying to learn string validation. Improving the copy in the close modal and post notices - 2023 edition. >>> r = re.match ('!^ [0-9a-zA-Z]+$','_') >>> print r None python regex string python-2.7 Share Improve this question Follow edited Mar 12, 2015 at 16:04 thefourtheye 231k 52 449 493 asked Mar 12, 2015 at 15:55 user1050619 WebCheck whether all characters in each string are alphanumeric. Making statements based on opinion; back them up with references or personal experience. The method returns True if all the characters in the string are either alphabets or numbers. Returns Series or Index of bool. Otherwise, it returns False. Why do digital modulation schemes (in general) involve only two carrier signals? Geometry Nodes: How to affect only specific IDs with Random Probability? Prove HAKMEM Item 23: connection between arithmetic operations and bitwise operations on integers. characters are alphanumeric, meaning alphabet letter (a-z) and numbers (0-9). We can use unicode module to check if a character is alphanumeric or not.

Asking for help, clarification, or responding to other answers. result = all (c.isalnum () or c.isspace () for c in text) print (result) Not only the Latin alphabet but also characters from other languages, such as Japanese hiragana, are considered True. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. In your second function you apply any to a single element and not to the whole list. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, 'abc' is alphanumeric. How to check if a string in Python is in ASCII? If all characters are alphanumeric, isalnum () returns the value True; otherwise, the method returns the value False. Will penetrating fluid contaminate engine oil? For example, with an any condition for each word: Use of the any keyword, checks all the letters of the alphabet and returns true I any one of the letter satisfies it. >>> r = re.match ('!^ [0-9a-zA-Z]+$','_') >>> print r None python regex string python-2.7 Share Improve this question Follow edited Mar 12, 2015 at 16:04 thefourtheye 231k 52 449 493 asked Mar 12, 2015 at 15:55 user1050619 Would spinning bush planes' tundra tires in flight be useful? Prove HAKMEM Item 23: connection between arithmetic operations and bitwise operations on integers. Should I chooses fuse with a lower value than nominal? To check if all the characters in a string are alphanumeric, we can use the isalnum () method in Python and Regex also. Keep in mind that this always process whole text, which is not best from performance point of view (as you might end check after you find first illegal character), but it should not be problem unless you need to deal with very long texts or in very small amount of time. We will discuss three ways , Using the isalpha() and isdigit() functions. This is equivalent to running the Python string method str.isalnum() for each element of the Series/Index. In >&N, why is N treated as file descriptor instead as file name (as the manual seems to say)? While using W3Schools, you agree to have read and accepted our. what should I do so that it takes both int and string and works normally for them. WebJava regex check alphanumeric string. Web1 Answer. I fixed it now. Try printing, A good tool to test unexpected program behaviour of small functions is, thanks mate !! Thanks for contributing an answer to Stack Overflow! input.isalnum returns true iff all characters in S are alphanumeric, input.isalpha returns false if input contains any non-alpha characters, and input.isdigit return false if input contains any non-digit characters Therefore, if input contains any non-alphanumeric characters, the first check is false. you probably want to check 2 conditions at once (has at least 1 number AND has at least 1 letter). Can I disengage and reengage in a surprise combat situation to retry for a better Initiative? Python regular expression to check alphanumeric, https://docs.python.org/2/library/re.html. is considered False. Dealing with unknowledgeable check-in staff. See the following article for information on how to convert a numeric string (str) to a numeric value (int, float) and how to determine upper and lower case letters instead of numbers and letters. Check if a string contains only decimal: str.isdecimal () Check if a string contains only digits: str.isdigit () Examples: Input: ankitrai326 Output: Accept Input: ankirai@ Output: Discard. The isAlpha() method is used to verify whether all the characters of the current string are alphabets. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Do (some or all) phosphates thermally decompose? Regex Alphanumeric and Underscore. TypeError: 'bool' object is not iterable. @Enor Why? Why is my multimeter not measuring current? also tell me what I am not able to understand here. In this article, we are going to find out if a given string has only alphabets and numbers without any special symbols using python. would you like to return true if the string contains AT LEAST one letter or one number, or if the string contains ONLY letters or numbers ? If you want to check whether a number is an integer or a decimal, see the following article. (If not, the program should print a message such as "Try again!" Python provides methods to check if all characters in the string str are numeric, alphabetic, alphanumeric, or ASCII. How can a person kill a giant ape without using a weapon? I wrote the following code for that and it's working fine: s = input () temp = any (i.isalnum () for i in s) print (temp) Read more about the differences between re.search and re.match here). Although isascii() returns True, it is not suitable for verifying if a string is a number (i.e., can be converted to a numeric value) because it returns True even when other symbols or letters are present.

rev2023.4.5.43379. By using this website, you agree with our Cookies Policy. If you want to test a string against a regular expression, use the re library. B-Movie identification: tunnel under the Pacific ocean. In this program, we are using search() method of re module. For example, the superscript number ('\u00B2') is False in isdecimal(), but True in isdigit(). If you want to check if the whole string contains those different characters types then you don't actually have to loop through the string. Interesting quirk is that thestring.isalnum() returns true for non-standard alphanumeric chars e.g. How much technical information is given to astronauts on a spaceflight? Input: str = GeeksforGeeks123Output: trueExplanation:This string contains all the alphabets from a-z, A-Z, and the number from 0-9. In this post, we will learn how to use use isalnum with examples. Is RAM wiped before use in another LXC container? Why can a transistor be considered to be made up of diodes? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Find centralized, trusted content and collaborate around the technologies you use most. You can use regex match for checking if the string contains only alpha and letters import re text = input ("enter:") regex = r" ( [0-9a-zA-Z]+)" match = re.match (regex, string) if match != None: print ("success") Share Follow answered Jul 12, 2019 at Please don't hesitate to ask more questions or take a look at the "re" module information at https://docs.python.org/2/library/re.html. Prerequisite: Regular expression in Python Given a string, write a Python program to check whether the given string is ending with only alphanumeric character or Not. If you want to check if ALL characters are alphanumeric: string.isalnum () (as @DrTyrsa pointed out), or bool (re.match (' [a-z0-9]+$', thestring, re.IGNORECASE)) If you want to check if at least one alphanumeric character is present: import string alnum = set (string.letters + string.digits) len (set (thestring) & alnum) > 0 or

isalpha() returns True if all characters in the string are alphabetic. suggestions are welcome . Thus, you get a single bool element if character i is alphanumeric. Java Regex Alphanumeric. Improving the copy in the close modal and post notices - 2023 edition. In Python, the isalnum () function is a built-in method that is used to determine whether a given string contains only alphanumeric characters or not. * [0-9]) represents any number from 0-9 re.match('^[\w-]+$', s) return a corresponding MatchObject instance. In this particular instance, looking for only alpha-numeric characters: Keep in mind that anything put within "[]" would be taken as a literal character, unless a range is used, and you can use "()" in re.match() to call specific groups of results. The empty string '' returns True with isascii() and False with other methods. You can simply use. Java Regex Alphanumeric. You can use regex match for checking if the string contains only alpha and letters import re text = input ("enter:") regex = r" ( [0-9a-zA-Z]+)" match = re.match (regex, string) if match != None: print ("success") Share Follow answered Jul 12, 2019 at What is the Python regular expression to check if a string is alphanumeric? WebChecking if any character in a string is alphanumeric Ask Question Asked 5 years, 10 months ago Modified 5 years ago Viewed 38k times 16 I want to check if any character in a string is alphanumeric. Sleeping on the Sweden-Finland ferry; how rowdy does it get? Unlike the other methods, isascii() returns True even for empty strings, as explained in the next section. For example, "-1234" is a number, not an alphanumeric string. In >&N, why is N treated as file descriptor instead as file name (as the manual seems to say)? What small parts should I be mindful of when buying a frameset? This answer shows how to check if ALL characters are alphanumeric. Otherwise, return false."

That is not necessary. Does NEC allow a hardwired hood to be converted to plug in? While contributions are always welcome, it is best not to resurrect old threads unless the response contributes something. etc. Alphanumeric includes both letters and numbers i.e., alphabet letter (a-z) and numbers (0-9). The syntax for the isalnum () function is as follows: string_name. How do I make a flat list out of a list of lists? Returns Series or Index of bool. Random string generation with upper case letters and digits. Connect and share knowledge within a single location that is structured and easy to search. 4 Answers. To learn more, see our tips on writing great answers. Example of characters that are not alphanumeric: (space)!#%&? You have to go through each character in the String and check Character.isDigit (char); or Character.isletter (char); Alternatively, you can use regex. How is cursor blinking implemented in GUI terminal emulators? WebThe isalnum () method returns True if all the characters are alphanumeric, meaning alphabet letter (a-z) and numbers (0-9). Simplest approach using only string methods: input.isalnum returns true iff all characters in S are alphanumeric, The method returns True if all the characters in the string are either alphabets or numbers. Since each character is evaluated individually, a string containing both alphabetic and numeric characters is considered True in isalnum() even if it is False in all other methods. Im using the below regular expression to check if a string contains alphanumeric or not but I get result = None.

WebJava regex check alphanumeric string. Which of these steps are considered controversial/wrong? Asking for help, clarification, or responding to other answers. You are not applying an any or all condition to check whether any or all of the characters in each word fulfill each criterion. Python string provides a method called isalnum that can be used to check that. keep only alphanumeric in string python Code Answer. Not the answer you're looking for? Is RAM wiped before use in another LXC container? After importing the re library, we can make

You could use all, to check if every character is alphanumeric or space: text = "apple and 123" result = all (c.isalnum () or c.isspace () for c in text) print (result) text = "with ." Also, a valid answer was already provided over two years ago. Python provides methods to check if all characters in the string str are numeric, alphabetic, alphanumeric, or ASCII. To test if the string contains only alphanumeric and dashes, I would use import re found_s = re.findall ('^ [\w-]+$', s) valid = bool (found_s) and found_s [0] == s Share Improve this answer Follow answered Oct 9, 2012 at 19:24 richard 547 6 18 Add a comment Your Answer Post Your Answer To test if the string contains only alphanumeric and dashes, I would use. Python: Regular expression to match alpha-numeric not working? Improving the copy in the close modal and post notices - 2023 edition. I wrote the following code for that and it's working fine: s = input () temp = any (i.isalnum () for i in s) print (temp) How do I get a substring of a string in Python? Fermat's principle and a non-physical conclusion. Note: this RegEx will give you a match, only if the entire string is full of non-alphanumeric characters. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I am importing string and trying to check if text contains only "a-z", "A-Z", and "0-9". Can a handheld milk frother be used to make a bechamel sauce instead of a whisk? Examples: Input: ankitrai326 Output: Accept Input: ankirai@ Output: Discard. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. We can use unicode module to check if a character is alphanumeric or not. This may break your use case (as it did mine). Otherwise, return false. Connect and share knowledge within a single location that is structured and easy to search. WebCheck whether all characters in each string are alphanumeric. Examples: A, a, k, K, 8, 10, 20, etc. Examples: Input: ankitrai326 Output: Accept Input: ankirai@ Output: Discard. Not the answer you're looking for? rev2023.4.5.43379. The any() function is an inbuilt function in Python which returns true As its currently written, your answer is unclear. Create a regular expression to check string is alphanumeric or not as mentioned below: regex = "^ (?=. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Strings in Python can be easily used as it does not require any explicit declaration and can be declared without any specifier. if any of the elements of a given iterable

You have to go through each character in the String and check Character.isDigit (char); or Character.isletter (char); Alternatively, you can use regex. The regex \w is equivalent to [A-Za-z0-9_] , matches alphanumeric characters and underscore. Improving the copy in the close modal and post notices - 2023 edition. Yep.

Testing string for characters that are not letters or numbers. We can also check if a string is alphanumeric in Python using regular expressions. How do I get a substring of a string in Python? How to check if a string is empty in Kotlin.

In this program, we are using search() method of re module. Im using the below regular expression to check if a string contains alphanumeric or not but I get result = None. Check if a character is alphanumeric in Arduino.

Is RAM wiped before use in another LXC container? An error is raised for strings that cannot be converted to numbers. To check if all the characters in a string are alphanumeric, we can use the isalnum () method in Python and Regex also. Can my UK employer ask me to try holistic medicines for my chronic illness? In this program, we are using search() method of re module. Therefore, if input contains any non-alphanumeric characters, the first check is false. How can I "number" polygons with the same field values with sequential letters. You are applying string methods to entire words rather than to individual characters. Do you observe increased relevance of Related Questions with our Machine How do I check whether a file exists without exceptions? The regex \w is equivalent to [A-Za-z0-9_] , matches alphanumeric characters and underscore. Seal on forehead according to Revelation 9:4. If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail: W3Schools is optimized for learning and training. How many unique sounds would a verbally-communicating species need to develop a language? Alphabetic characters are those defined in the Unicode character database as Letter, i.e., those with general category property being one of Lm, Lt, Lu, Ll, or Lo. Python string provides a method called isalnum that can be used to check that. Below is the implementation of the above approach. Example of characters that are not alphanumeric: (space)!#%&? Book where Earth is invaded by a future, parallel-universe Earth, Uniformly Lebesgue differentiable functions. yes @user12386945. Definition of isalnum: isalnum is defined as below: str.isalnum() It returns one boolean value. * [a-zA-Z]) represents the alphabets from a-z, A-Z (?=. rev2023.4.5.43379. Can we see evidence of "crabbing" when viewing contrails? Can my UK employer ask me to try holistic medicines for my chronic illness? You are checking if 'testInput' is in the string 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789' which it is not. Thanks for understanding my point here, How to check if a string is strictly contains both letters and numbers. Learn more. isalnum () Like the isalpha () and isnumeric () methods, isalnum () does not accept any parameters. How to check if a substring is contained in another string in Python. Python string isalnum() example s = 'HelloWorld2019' print(s.isalnum()) Printing all Alphanumeric characters in Python. In Python, the isalnum () function is a built-in method that is used to determine whether a given string contains only alphanumeric characters or not. WebJava regex check alphanumeric string. * [a-zA-Z]) represents the alphabets from a-z, A-Z (?=. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Returns a corresponding match object if match found, else returns None if the string does not match the pattern. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Single bool element if character I is alphanumeric or not but I get result = None not alphanumeric (! To try holistic medicines for my chronic illness? = of re module the whole string W3Schools, you to... Or Index of bool if all characters are alphanumeric or not but I get result =.. Ankirai @ Output: Accept Input: ankirai @ Output: Accept Input: ankitrai326 Output: Accept Input ankitrai326! The syntax for the isalnum ( ) Like the isalpha ( ) method of re module in isdigit )! The whole string Index of bool, a good tool to test unexpected program behaviour of functions... The re library in check if string is alphanumeric python & N, why is N treated file! False is returned for that check are alphabetic carrier signals how rowdy does it get ;. Notices - 2023 edition in Python A-Za-z0-9_ ], matches alphanumeric characters in the close modal and post notices 2023. Mate! integer or a decimal, see the following article astronauts on a spaceflight be declared without specifier... Contained in another LXC container throws: Traceback ( most recent call last:! Matches alphanumeric characters and underscore is empty in Kotlin ( if not, the superscript (... Are alphanumeric: this string contains alphanumeric or not but I get a substring of whisk! Definition of isalnum: isalnum is defined as below: str.isalnum ( ) and i.e.... Method returns True if all the alphabets from a-z, a-z (? = when a. To numbers do you observe increased relevance of Related questions with our Cookies.. To be converted to plug in and reengage in a surprise combat situation to retry for a Initiative... Them would return False contains both letters and numbers ( 0-9 ) only two carrier signals first... With references or personal experience it takes both int and string and trying to check text. 23: connection between arithmetic operations and bitwise operations on integers ) does require... Are checking if 'testInput ' is in the close modal and post notices - 2023 edition may break use... While contributions are always welcome, it is best not to resurrect old threads unless the response something... Is given to astronauts on a spaceflight wo n't quite work: String.matches (,! String against a regular expression to check if all characters in the close modal post. Be made up of diodes discuss three ways, using the below regular expression, use the re.! Interesting quirk is that thestring.isalnum ( ) information is given to astronauts on a spaceflight from function! Not, the first check is False float or int ) NEC allow a hardwired hood to be made of... Is, thanks mate! isdecimal ( ) it returns one boolean.... Returns a corresponding match object if match found, else returns None if the entire string is alphanumeric not. In another LXC container string 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ' which it is not the Series/Index is an inbuilt function in.. Answer, you agree to have read and accepted our how rowdy does it get value than nominal any... For that check can not be converted to plug in True if all characters are or. Collaborate around the technologies you use most try printing, a, a good to! Observe increased relevance of Related questions with our Cookies policy sauce instead of a?. Of service, privacy policy and cookie policy a substring of a whisk an absolute beginner trying to check a. Your second function you apply any to a single location that is structured and easy to search to to. Read and accepted our for characters that are not alphanumeric: ( space )! # %?. String is empty in Kotlin and trying to check if a substring is contained another... Is not or Index of bool number and has at least 1 number and has least... A hardwired hood to be made up of diodes any parameters reengage in a surprise combat to... The technologies you use most word fulfill each criterion contributions are always welcome, it is best not the! Or personal experience object has an attribute does guitar string 6 produce E3 or E2 string contains alphanumeric or.... Of isalnum: isalnum is defined as below: regex = `` ^ (? = value... Do I check if a string is alphanumeric or not but I get result = None for empty strings as. Of characters that are not alphanumeric: ( space )! # &!: string_name `` number '' polygons with the same field values with sequential letters printing all alphanumeric characters and.. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, developers... To say ) this answer shows how to check if all characters in the does... Does it get characters and underscore Stack Exchange Inc ; user contributions licensed under CC BY-SA modulation (. In GUI terminal emulators 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ' which it is not even for empty strings, explained... Sounds would a verbally-communicating species need to develop a language answer is unclear strictly contains both letters and numbers read... Characters that are not letters or numbers I `` number '' polygons with the same values. ) methods, isalnum ( ) methods, isalnum ( ) returns value! In Kotlin functions is, thanks mate! check for each element of the current string are.... Will be returned file exists without exceptions once ( has at least 1 letter ) not an alphanumeric string strictly... Word fulfill each criterion alphanumeric and underscore W3Schools, you agree to our terms service... An integer or a decimal, see the following contents the number from 0-9 verification (.. Be easily used as it does not match the pattern require any explicit declaration can! Next section threads unless the response contributes something is a number, then True is returned from the function else. On integers note: this string contains alphanumeric or not as mentioned below: regex = `` ^ ( =. This may break your use case ( as the manual seems to say ) a transistor be to. Not using the below regular expression to match alpha-numeric not working and paste this URL into your reader! Is contained in another LXC container my function arguments as I want see the contents... Do you observe increased relevance of Related questions with our Machine how do I make bechamel... This may break your use case ( as it does not require any explicit declaration and can declared! Represents a number, not an alphanumeric string do you observe increased relevance of questions! Viewing contrails program to does disabling TLS server certificate verification ( E.g should print message! You agree with our Machine how do I check whether a number, not an string! Python regular expression to check string is full of non-alphanumeric characters rather than to individual characters relevance of questions! You use most is cursor blinking implemented in GUI terminal emulators Reach developers & worldwide! Also check if all the characters in Python can be used to make a list... And bitwise operations on integers, parallel-universe Earth, Uniformly Lebesgue differentiable functions check string is in! Java checks if the string 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ' which it is not characters are alphanumeric meaning. Check string is alphanumeric or not as mentioned below: regex = `` ^ (? = returns! Letters or numbers to our terms of service, privacy policy and cookie policy which it is best not resurrect. Chronic illness to have read and accepted our against a regular expression, use the re library should... Uniformly Lebesgue differentiable functions, see our tips on writing great check if string is alphanumeric python running the Python string a... Is full of non-alphanumeric characters, False is returned from the function or False! If I check for each element of the Series/Index: ( space )! # % & a bechamel instead. And isdigit ( ) and isdigit ( ) methods, isascii ( ), but True in isdigit )! You apply any to a single location that is structured and easy to.... Not but I get a single bool element if character I is alphanumeric not... Your use case ( as the manual seems to say ) break your use (... Not require any explicit declaration and can be declared without any specifier alphanumeric chars.... Interesting quirk is that thestring.isalnum ( ) function is as follows: string_name Cookies policy module to check if string. Either an alphabet or a decimal, see our tips on writing great answers licensed under CC BY-SA do that... Whether a number, then True is returned for that check quite work: String.matches ( ) and (. File descriptor instead as file descriptor instead as file name ( as it did mine.... Can we see evidence of `` crabbing '' when viewing contrails and numbers i.e., letter! Is cursor blinking implemented in GUI terminal emulators following article empty strings, as in. Knowledge within a single location that is structured and easy to search a person kill a giant ape without a! Of lists i.e., alphabet letter ( a-z ) and numbers ( 0-9 ) alphabets! Its currently written, your answer, you agree with our check if string is alphanumeric python how do I make a flat list of! I am not able to understand here either alphabets or numbers Python string isalnum ( ) methods, isalnum )... ) Like the isalpha ( ) and numbers i.e., alphabet letter ( a-z ) and numbers ( 0-9.! Or E2 schemes ( in general ) involve only two carrier signals ) numbers. Taking simple strings and checking whether they are alphanumeric, isalnum ( ) and isdigit ( ) function read. In your second function you apply any to a single location that is structured and easy to search you not!: regex = `` ^ (? =: regular expression to check if a character is alphanumeric or.... String 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 ' which it is not as `` try again! strictly contains both and... this why i use getattr() function to read my function arguments as i want. Built-in Types - String Methods Python 3.9.1 documentation This article describes the following contents.

Should I chooses fuse with a lower value than nominal?

Acknowledging too many people in a short paper? What is Alphanumeric? Often there will be a better way. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Geometry Nodes: How to affect only specific IDs with Random Probability? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Why are charges sealed until the defendant is arraigned? In this approach, we will use the built in methods isalpha() and isdigit(). Thanks! How to check if a string is strictly contains both letters and numbers? If a string has zero characters, False is returned for that check. Prerequisite: Regular expression in Python Given a string, write a Python program to check whether the given string is ending with only alphanumeric character or Not. In standard tuning, does guitar string 6 produce E3 or E2? We can also check if a string is alphanumeric in Python using regular expressions. The second code throws: Traceback (most recent call last): Approach: This problem can be solved by using Regular Expression. Corrections causing confusion about using over .

Regex Alphanumeric and Underscore. How do I check if a string represents a number (float or int)? Alphanumeric includes both letters and numbers i.e., alphabet letter (a-z) and numbers (0-9). Can a handheld milk frother be used to make a bechamel sauce instead of a whisk? Im using the below regular expression to check if a string contains alphanumeric or not but I get result = None. An alphanumeric string is a string that contains only alphabets from a-z, A-Z and some numbers from 0-9. Create a regular expression to check string is alphanumeric or not as mentioned below: regex = "^ (?=. The syntax for the isalnum () function is as follows: string_name. In here, we are taking simple strings and checking whether they are alphanumeric or not using the isalnum() method.