To put it another way, when in doubt, use parenthesis.
The regular expression first match at the initial position of string , giving the result set (the second is because of the subexpression marked by the parentheses). As the length of the match is 0, we do not advance to the next position yet.
The context specifies how parenthesis are used.
Return a tuple containing all the subgroups of the match, from 1 up to howevermany groups are in the pattern. The default argument is used for groups thatdid not participate in the match; it defaults to .
Returns one or more subgroups of the match. If there is a single argument, theresult is a single string; if there are multiple arguments, the result is atuple with one item per argument. Without arguments, group1 defaults to zero(the whole match is returned). If a groupN argument is zero, the correspondingreturn value is the entire matching string; if it is in the inclusive range[1..99], it is the string matching the corresponding parenthesized group. If agroup number is negative or larger than the number of groups defined in thepattern, an exception is raised. If a group is contained in apart of the pattern that did not match, the corresponding result is .If a group is contained in a part of the pattern that matched multiple times,the last match is returned.
Matching parentheses | Thoughts
In the later examples we have started to see just how complicated regular expressions can get. These examples are not the half of it. It is possible to do some almost absurdly difficult-to-understand things with regular expression (but ones that are nonetheless useful).
Jan 05, 2011 · Matching parentheses
Executes a regular expression matching, and returns or . The regular expression can be specified either as in which case it is automatically compiled (as by ) and executed, or as a precompiled in which case it is executed against the subject directly. When compilation is involved, exception is thrown if a compilation error occurs. Call to get information about the location of the error in the regular expression. If the regular expression is previously compiled, the option list can only contain the following options: Otherwise all options valid for function are also allowed. Options allowed both for compilation and execution of a match, namely and , affect both the compilation and execution if present together with a non-precompiled regular expression. If the regular expression was previously compiled with option , is to be provided as a valid Unicode , otherwise any will do. If compilation is involved and option is specified, both and the regular expression are to be specified as valid Unicode . defines what to return from the function upon successful matching. The tuple can contain both a value specification, telling which of the captured substrings are to be returned, and a type specification, telling how captured substrings are to be returned (as index tuples, lists, or binaries). The options are described in detail below. If the capture options describe that no substring capturing is to be done (), the function returns the single atom upon successful matching, otherwise the tuple . Disabling capturing can be done either by specifying or an empty list as . Option adds the possibility that an error tuple is returned. The tuple either indicates a matching error ( or ), or a compilation error, where the error tuple has the format . Notice that if option is not specified, the function never returns error tuples, but reports compilation errors as a exception and failed matches because of exceeded match limits simply as . The following options are relevant for execution: For a descriptions of options only affecting the compilation step, see .
Parenthesis Matching in Emacs - Daniel Han's Technical …
However because of this, the virtual canvas of the first image will controlthe output image size, and other image will be overlaid into that image area.
Python program to check matching of simple parentheses
Exception raised when a string passed to one of the functions here is not avalid regular expression (for example, it might contain unmatched parentheses)or when some other error occurs during compilation or matching. It is never anerror if a string contains no match for a pattern. The error instance hasthe following additional attributes: