What does PQE mean in UNCLASSIFIED
PQE stands for Pattern Quantification Exception. It refers to an exception that arises when a regular expression pattern matches more or fewer occurrences of a particular subpattern than expected.
PQE meaning in Unclassified in Miscellaneous
PQE mostly used in an acronym Unclassified in Category Miscellaneous that means Pattern Quantification Exception
Shorthand: PQE,
Full Form: Pattern Quantification Exception
For more information of "Pattern Quantification Exception", see the section below.
Characteristics of PQE
- Occurs when a quantifier (e.g., *, +, ?, {}) in a regular expression matches an unexpected number of occurrences of a subpattern.
- Can lead to unpredictable and unintended matching behavior.
- Common in cases where the quantifier is used to match optional or variable-length subpatterns.
Example
Consider the following regular expression:
.*\d{2}This pattern is intended to match any string that contains a sequence of two digits. However, it will also match strings with more than two digits, such as "1234". This behavior is caused by the PQE associated with the quantifier *, which allows the preceding subpattern .* to match any number of characters (including zero).
Prevention and Mitigation
- Use specific quantifiers: Use quantifiers that explicitly define the expected number of occurrences (e.g.,
{2}to match exactly two occurrences). - Consider using non-greedy quantifiers: Non-greedy quantifiers (e.g.,
*?,+?) match as few occurrences as possible, thus reducing the risk of PQE. - Test and validate patterns: Thoroughly test regular expression patterns to ensure they produce the desired matching behavior and do not encounter PQE.
Essential Questions and Answers on Pattern Quantification Exception in "MISCELLANEOUS»UNFILED"
What is a Pattern Quantification Exception (PQE)?
A Pattern Quantification Exception (PQE) is an exception that can be used to exclude certain patterns from being quantified by a regular expression. This can be useful when you want to prevent the regular expression from matching patterns that you don't want it to match.
What is the syntax for a PQE?
The syntax for a PQE is as follows:
(?#
pattern
)where:
(?#is the opening delimiter for the PQE.patternis the pattern that you want to exclude from being quantified.)is the closing delimiter for the PQE.
How do I use a PQE?
To use a PQE, you can simply insert it into the regular expression where you want to exclude the specified pattern from being quantified. For example, the following regular expression will match any word that contains the letter "a", but it will not match any word that contains the pattern "aa":
^[a-zA-Z]+(?#aa)[a-zA-Z]+$Final Words: PQE is a potential issue in regular expression patterns that can lead to unexpected matching behavior. By understanding its causes and implementing preventive measures, developers can ensure that their patterns are robust and reliable.
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