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object --+ | ParserElement --+ | ParseElementEnhance --+ | PrecededBy
Lookbehind matching of the given parse expression.
PrecededBy
does not advance the parsing position within the
input string, it only verifies that the specified parse expression
matches prior to the current position. PrecededBy
always
returns a null token list, but if a results name is defined on the given
expression, it is returned.
Parameters:
None
) - (int) maximum number of
characters to lookbehind prior to the current parse location
If the lookbehind expression is a string, Literal, Keyword, or a Word or CharsNotIn with a specified exact or maximum length, then the retreat parameter is not required. Otherwise, retreat must be specified to give a maximum number of characters to look back from the current parse position for a lookbehind match.
Example:
# VB-style variable names with type prefixes int_var = PrecededBy("#") + pyparsing_common.identifier str_var = PrecededBy("$") + pyparsing_common.identifier
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