We use re.findall or re.finditer methods to find all matches to a regular method.re.findall(pattern, string) returns a list of matching strings.re.finditer(pattern, string) returns an iterator over MatchObject object

The following code gets the number of captured groups using Python regex in given stringExampleimport re m = re.match(r"(\d)(\d)(\d)", "632") print len(m.groups())OutputThis gives the output3

When the match method is implemented, if it turns out that there are no matches, then None is returned. There are no functions in the re module that throw up an exception when the list or matches is emptyexception re.errorException raised when a string passed to one of the functions here is not a valid regular expression (for example, it might contain unmatched parentheses) or when some other error occurs during compilation or matching. It is never an error if a string contains no match for a pattern.

Presently, when regular expressions are compiled, the result is cached so that if the same regex is compiled again, it is retrieved from the cache and no extra effort is required. This cache supports up to 100 entries. Once the 100th entry is reached, the cache is cleared and a new compile must occur.The objective of caching is to decrease the average call time of the function. The overhead associated with keeping more information in _cache and paring it instead of clearing it would increase that average call time. The _cache.clear() call will complete quickly, and even though cache is ... Read More

re.match(), re.search(), and re.findall() are methods of the Python module re (Python Regular Expressions). The re.match() method The re.match() method finds match if it occurs at start of the string. For example, calling match() on the string ‘TP Tutorials Point TP’ and looking for a pattern ‘TP’ will match.   Example import re result = re.match(r'TP', 'TP Tutorials Point TP') print result.group(0) Output TP The re.search() method The re.search() method is similar to re.match() but it doesn’t limit us to find matches at the beginning of the string only.  Example import re result = re.search(r'Tutorials', 'TP Tutorials Point TP') ... Read More

You will study regular expressions (RegEx) in this blog and interact with RegEx using Python's re-module (with the help of examples). A Regular Expression (RegEx) is a sequence of characters that defines a search pattern. For example, ^a...s$ A RegEx pattern is defined by the code above. Any five-letter string with an a and a s at the end forms the pattern. Python has a module named re to work with RegEx. Here's an example − import re pattern = '^a...s$' test_string = 'abyss' result = re.match(pattern, test_string) if result: print("Search successful.") else: ... Read More

According to Python documentationPython does not currently have an equivalent to scanf(). Regular expressions are generally more powerful, though also more verbose, than scanf() format strings. The table below offers some more-or-less equivalent mappings between scanf() format tokens and regular expressions.scanf() TokenRegular Expression%c.%5c.{5}%d[-+]?\d+%e, %E, %f, %g[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?%i[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)%o[-+]?[0-7]+%s\S+%u\d+%x, %X[-+]?(0[xX])?[\dA-Fa-f]+To extract the filename and numbers from a string like/usr/sbin/sendmail - 0 errors, 4 warningsyou would use a scanf() format like%s - %d errors, %d warningsThe equivalent regular expression would be(\S+) - (\d+) errors, (\d+) warningsRead More

The most basic regex features are nearly the same in nearly every implementation: wild character ., quantifiers *, +, and ?, anchors ^ and $, character classes inside [], and back references \1, \2, \3etc.Alternation is denoted | in Perl and PythonPerl and Python will let you modify a regular expression with (?aimsx). For example, (?i) makes an expression case-insensitive. These modifiers have the same meaning on both languages. Also, both languages let you introduce a comment in a regular expression with (?# … ).Perl and Python support positive and negative look-around with the same syntax: (?=), (?!), (?Both languages ... Read More

Special character dot '.'(Dot.) In the default mode, this matches any character except a newline. If the DOTALL flag has been specified, this matches any character including a newline.Special character '?'Causes the resulting RE to match 0 or 1 repetitions of the preceding RE. ab? will match either ‘a’ or ‘ab’Special character asterisk'*"Causes the resulting RE to match 0 or more repetitions of the preceding RE, as many repetitions as are possible. ab* will match ‘a’, ‘ab’, or ‘a’ followed by any number of ‘b’s.

Here are two basic examples of Python regular expressionsThe re.match() method finds match if it occurs at start of the string. For example, calling match() on the string ‘TP Tutorials Point TP’ and looking for a pattern ‘TP’ will match. However, if we look for only Tutorials, the pattern will not match. Let’s check the code.Exampleimport re result = re.match(r'TP', 'TP Tutorials Point TP') print resultOutputThe re.search() method is similar to re.match() but it doesn’t limit us to find matches at the beginning of the string only. Unlike in re.match() method, here searching for pattern ‘Tutorials’ in the string ‘TP ... Read More