A Re gular Ex pression RegEx is a sequence of characters that defines a search pattern. For example. The above code defines a RegEx pattern. The pattern is: any five letter string starting with a and ending with s. Here, we used re. The method returns a match object if the search is successful. If not, it returns None. There are other several functions defined in the re module to work with RegEx.
Before we explore that, let's learn about regular expressions themselves. To specify regular expressions, metacharacters are used. Metacharacters are characters that are interpreted in a special way by a RegEx engine. Here's a list of metacharacters:. Here, [abc] will match if the string you are trying to match contains any of the ab or c.
The question mark symbol? This means at least nand at most m repetitions of the pattern left to it. Let's try one more example. Parentheses is used to group sub-patterns. For example, a b c xz match any string that matches either a or b or c followed by xz. This makes sure the character is not treated in a special way. Special sequences make commonly used patterns easier to write. Here's a list of special sequences:. Matches if the specified characters are not at the beginning or end of a word.
Tip: To build and test regular expressions, you can use RegEx tester tools such as regex This tool not only helps you in creating regular expressions, but it also helps you learn it. Python has a module named re to work with regular expressions. To use it, we need to import the module. The re. If the pattern is not found, re. You can pass maxsplit argument to the re.In this article you will learn how to match numbers and number range in Regular expressions. The Regex number range include matching 0 to 9, 1 to 9, 0 to 10, 1 to 10, 1 to 12, 1 to 16 and, ,and The first important thing to keep in mind about regular expressions is that they don't know numbers, they don't know counting and they can not comprehend means any number from 1 to The reason is regex deals with text only and not numbers, hence you have to take a little care while dealing with numbers and number ranges or numeric ranges in regex match, search, validate or replace operations.
This video course teaches you the Logic and Philosophy of Regular Expressions for different number ranges. Just for an example, lets say if you want to match any number from 1 to and you write regex for it as. This regex will match only two numbers, yes, only two numbers and NO doubt about that. Can you figure out which two numbers? Similarly the range  will match 0,1,2,5.
First is the range which is in a character class will match 0,1,2 and 5 written two times, will match 5. Now lets begin the logic and philosophy of matching numbers and number ranges in Regular expressions. The simplest match for numbers is literal match. But you can see its not flexible as it is very difficult to know about a particular number in text or the number may occur in ranges.
It will match any single digit number from 0 to 9. Instead of writing the shorthand version is  where  is used for character range. But if you want to match number of any number of digits like 2,55, a quantifier is added at the end. Now about numeric ranges and their regular expressions code with meaning. To match numeric range of i. To match any number from 1 to 9, regular expression is simple.
To match numbers from 0 to 10 is the start of a little complication, not that much, but a different approach is used. This series is broken in to two components. Here the range from is divided in to three components per requirement. Here the range is divided in to three components, and the additional component then the previous range is number The second part is and regex for this part is.
For more details please see regex for ip address. The regex for range 0 to is split in to three sections. Regex for Numbers and Number Range In this article you will learn how to match numbers and number range in Regular expressions.
In most programming languages where it is supported. The  has no possible misinterpretations, [[:digit:]] is available in more utilities and in some cases mean only . As for the meaning of range expressions is only defined by POSIX in the C locale; in other locales it might be different might be codepoint order or collation order or something else.
That is painfully false in some instances: Linux in some locale that is not "C" June of systems, for example:. That sed has some troubles. Should remove only but removes almost all digits.
That means that it accepts most digits but not some nine's??? There are many languages: Perl, Java, Python, C. For example, this perl code will match all the digits from above:. Which is equivalent to select all characters that have the Unicode properties of Numeric and digits :.
Which grep could reproduce the specific version of pcre may have a different internal list of numeric code points than Perl :.
But wait, there's more! This is similar to the difference in C between isdigit 3  and isnumber 3 [ plus whatever else from the locale. There may be calls that can be made to obtain the value of the digit, even if it is not  :. Here I would like to add differences in implementation of regex engine. In grep's manual it's mentioned that [[:digit:]] is just in the C locale. The theoretical differences have already been pretty well explained in the other answers, so it remains to explain the practical differences.
Often, when you want to crunch some numbers, the numbers themselves are in an awkwardly formatted text file. You want to extract them for use in your program. You can probably tell the number format by looking at the file and your current locale, so it's ok to use any of the formsas long as it gets the job done.
You have some untrusted user input maybe from a web formand you need to make certain it doesn't contain any surprises.
Maybe you want to store it in a numeric field in a database, or use as a parameter to a shell command to run on a server. In this case, you really want since it's the most restrictive and predictable one.
You have a bit of data that you are not going to use for anything "dangerous", but it would nice to know if it's a number. For example, your program allows the user to input an address, and you want to highlight a possible typo if the input doesn't contain a house number. In this case, you probably want to be as broad as possible, so [[:digit:]] is the way to go. Those would seem to be the three most common use cases for digit matching.
I'd like to extractbut not This might be solved by negative lookahead, but I was not able to find the right solution. Note that this will only work when the country code is two digits as in your example. To support country codes with one or 3 digits, things get a little tricky because python doesn't support Lookbehinds with non-fixed width.
You could, however, use multiple Lookbehinds like this:. Learn more. Regex for 9-digit number that does not start from the country code like prefix [closed] Ask Question.
Asked 14 days ago. Active 13 days ago. Viewed 61 times. Mykola Pavlov. Mykola Pavlov Mykola Pavlov 1 1 gold badge 7 7 silver badges 9 9 bronze badges. For example, the country Anguilla has the code Thank you. Active Oldest Votes. Use a negative Lookbehind:? You could, however, use multiple Lookbehinds like this:?
Wow, I knew about the look ahead feature but never thought there also a look behind. Thank you so much. I suggest using re. Here is an explanation of the regex used:? Tim Biegeleisen Tim Biegeleisen k 18 18 gold badges silver badges bronze badges. Thanks for explaining this, I learned a lot about look behind.
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This behaviour will happen even if it is a valid escape sequence for a regular expression. Usually patterns will be expressed in Python code using this raw string notation. It is important to note that most regular expression operations are available as module-level functions and methods on compiled regular expressions. The third-party regex module, which has an API compatible with the standard library re module, but offers additional functionality and a more thorough Unicode support.
Regex for Numbers and Number Range
A regular expression or RE specifies a set of strings that matches it; the functions in this module let you check if a particular string matches a given regular expression or if a given regular expression matches a particular string, which comes down to the same thing.
Regular expressions can be concatenated to form new regular expressions; if A and B are both regular expressions, then AB is also a regular expression.
In general, if a string p matches A and another string q matches Bthe string pq will match AB. This holds unless A or B contain low precedence operations; boundary conditions between A and B ; or have numbered group references.
Thus, complex expressions can easily be constructed from simpler primitive expressions like the ones described here. For details of the theory and implementation of regular expressions, consult the Friedl book [Frie09]or almost any textbook about compiler construction.
A brief explanation of the format of regular expressions follows. Regular expressions can contain both special and ordinary characters. Most ordinary characters, like 'A''a'or '0'are the simplest regular expressions; they simply match themselves. You can concatenate ordinary characters, so last matches the string 'last'. Some characters, like ' ' or ' 'are special. Special characters either stand for classes of ordinary characters, or affect how the regular expressions around them are interpreted.
This avoids ambiguity with the non-greedy modifier suffix? To apply a second repetition to an inner repetition, parentheses may be used. For example, the expression?
In the default mode, this matches any character except a newline. More interestingly, searching for foo. Causes the resulting RE to match 0 or more repetitions of the preceding RE, as many repetitions as are possible. Causes the resulting RE to match 1 or more repetitions of the preceding RE. Causes the resulting RE to match 0 or 1 repetitions of the preceding RE. Specifies that exactly m copies of the previous RE should be matched; fewer matches cause the entire RE not to match.
Causes the resulting RE to match from m to n repetitions of the preceding RE, attempting to match as many repetitions as possible.
Omitting m specifies a lower bound of zero, and omitting n specifies an infinite upper bound. The comma may not be omitted or the modifier would be confused with the previously described form.
Causes the resulting RE to match from m to n repetitions of the preceding RE, attempting to match as few repetitions as possible. This is the non-greedy version of the previous qualifier. However, if Python would recognize the resulting sequence, the backslash should be repeated twice. Characters can be listed individually, e. Ranges of characters can be indicated by giving two characters and separating them by a '-'for example [a-z] will match any lowercase ASCII letter,  will match all the two-digits numbers from 00 to 59and [A-Fa-f] will match any hexadecimal digit.
If - is escaped e. Special characters lose their special meaning inside sets. Characters that are not within a range can be matched by complementing the set.A RegEx, or Regular Expression, is a sequence of characters that forms a search pattern. Python has a built-in package called rewhich can be used to work with Regular Expressions. When you have imported the re module, you can start using regular expressions:. The re module offers a set of functions that allows us to search a string for a match:.
A set is a set of characters inside a pair of square brackets  with a special meaning:.Regular Expressions (RegEx) Tutorial #6 - Metacharacters
The search function searches the string for a match, and returns a Match object if there is a match. The split function returns a list where the string has been split at each match:.
Python RegEx – Extract or Find All the Numbers in a String
You can control the number of occurrences by specifying the maxsplit parameter:. The sub function replaces the matches with the text of your choice:. You can control the number of replacements by specifying the count parameter:. Note: If there is no match, the value None will be returned, instead of the Match Object. The Match object has properties and methods used to retrieve information about the search, and the result:. If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:.
LOG IN. New User? Sign Up For Free! Forgot password? Example Print the position start- and end-position of the first match occurrence. Example Print the part of the string where there was a match.
It provides a gentler introduction than the corresponding section in the Library Reference. Regular expressions called REs, or regexes, or regex patterns are essentially a tiny, highly specialized programming language embedded inside Python and made available through the re module.
Using this little language, you specify the rules for the set of possible strings that you want to match; this set might contain English sentences, or e-mail addresses, or TeX commands, or anything you like.
You can also use REs to modify a string or to split it apart in various ways. Regular expression patterns are compiled into a series of bytecodes which are then executed by a matching engine written in C.
For advanced use, it may be necessary to pay careful attention to how the engine will execute a given RE, and write the RE in a certain way in order to produce bytecode that runs faster. The regular expression language is relatively small and restricted, so not all possible string processing tasks can be done using regular expressions. There are also tasks that can be done with regular expressions, but the expressions turn out to be very complicated.
In these cases, you may be better off writing Python code to do the processing; while Python code will be slower than an elaborate regular expression, it will also probably be more understandable. For a detailed explanation of the computer science underlying regular expressions deterministic and non-deterministic finite automatayou can refer to almost any textbook on writing compilers. Most letters and characters will simply match themselves. For example, the regular expression test will match the string test exactly.
Instead, they signal that some out-of-the-ordinary thing should be matched, or they affect other portions of the RE by repeating them or changing their meaning. Much of this document is devoted to discussing various metacharacters and what they do. Characters can be listed individually, or a range of characters can be indicated by giving two characters and separating them by a '-'.
For example, [abc] will match any of the characters abor c ; this is the same as [a-c]which uses a range to express the same set of characters. If you wanted to match only lowercase letters, your RE would be [a-z]. Metacharacters are not active inside classes. You can match the characters not listed within the class by complementing the set. If the caret appears elsewhere in a character class, it does not have special meaning.
As in Python string literals, the backslash can be followed by various characters to signal various special sequences. ASCII flag when compiling the regular expression. For a complete list of sequences and expanded class definitions for Unicode string patterns, see the last part of Regular Expression Syntax in the Standard Library reference.
Matches any decimal digit; this is equivalent to the class . These sequences can be included inside a character class. The final metacharacter in this section is. Another capability is that you can specify that portions of the RE must be repeated a certain number of times.