By Paul McGuire
Have to extract facts from a textual content dossier or an internet web page? Or do you need to make your program extra versatile with user-defined instructions or seek strings? Do average expressions and lex/yacc make your eyes blur and your mind hurt?
Pyparsing may be the resolution. Pyparsing is a pure-Python type library that makes it effortless to construct recursive-descent parsers fast. there isn't any have to handcraft your individual parsing kingdom computer. With pyparsing, you could quick create HTML web page scrapers, logfile facts extractors, or complicated info constitution or command processors. This brief minimize exhibits you the way!
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Approximately This Book
• Simplify layout development implementation utilizing the ability of Python
• each one development is observed with a real-world instance demonstrating its key features
• this is often an easy-to-follow consultant targeting the sensible elements of Python layout patterns
Who This booklet Is For
This e-book is for Python programmers with an intermediate history and an curiosity in layout styles carried out in idiomatic Python. Programmers of alternative languages who're drawn to Python may also make the most of this e-book, however it will be higher in the event that they first learn a few introductory fabrics that designate how issues are performed in Python.
What you'll Learn
• discover manufacturing facility procedure and summary manufacturing facility for item creation
• Clone items utilizing the Prototype pattern
• Make incompatible interfaces appropriate utilizing the Adapter pattern
• safe an interface utilizing the Proxy pattern
• decide upon an set of rules dynamically utilizing the method pattern
• expand an item with no subclassing utilizing the Decorator pattern
• maintain the good judgment decoupled from the UI utilizing the MVC pattern
Python is an object-oriented, scripting language that's utilized in wide variety of different types. In software program engineering, a layout trend is a suggested method to a software program layout challenge. even if now not new, layout styles stay one of many most well-liked themes in software program engineering and so they come as a prepared reference for software program builders to resolve the typical difficulties they face at work.
This publication will take you thru each layout trend defined with assistance from real-world examples. the purpose of the publication is to introduce extra low-level element and ideas on how you can write Pythonic code, not only targeting universal strategies as carried out in Java and C++. It contains small sections on troubleshooting, most sensible practices, procedure structure, and its layout facets. With the aid of this booklet, it is possible for you to to appreciate Python layout trend suggestions and the framework, in addition to matters and their answer. You'll specialize in all sixteen layout styles which are used to resolve daily difficulties.
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Extra resources for Getting Started with Pyparsing
Binary operations in operatorPrecedence can return multiple operation/operands if multiple operations of the same precedence level occur together. For instance, a binary operation for addition will parse "a+b+c" as [ 'a', '+', 'b', '+', 'c' ], not Getting Started with Pyparsing 54 [[ 'a', '+', 'b' ], '+', 'c' ], so BinaryOperation needs to be able to recognize and process a chain of like operations, not just a simple a op b operation. The Python [0::2] slicing notation indicates that the operands will be taken from the list of tokens beginning with the 0th element, and then stepping by 2 until the end of the list.
Following our standard practice, we start by defining the BNF for an S-expression: alphaword ::= alphas+ integer ::= nums+ sexp ::= alphaword | integer | '(' sexp* ')' Getting Started with Pyparsing 36 The first two expressions are nothing new, and you can see how we would use pyparsing's Word class to define them: alphaword = Word(alphas) integer = Word(nums) But sexp is more difficult. Our dilemma is that the definition for sexp includes sexp itself, but to define sexp we need to refer to sexp!
In this version of the BNF, AND expressions will be parsed ahead of OR expressions, and NOT expressions will be parsed ahead of AND expressions. searchExpr ::= searchAnd [ OR searchAnd ]... searchAnd ::= searchTerm [ AND searchTerm ]... setParseAction( removeQuotes ) | \ Group( LPAREN + searchExpr + RPAREN ) ) searchAnd = Group( searchTerm + ZeroOrMore( and_ + searchTerm ) ) searchExpr << Group( searchAnd + ZeroOrMore( or_ + searchAnd ) ) Using this grammar, our parsing examples evaluate as: wood and blue or red [[['wood', 'and', 'blue'], 'or', ['red']]] wood and (blue or red) [[['wood', 'and', [[['blue'], 'or', ['red']]]]]] (steel or iron) and "lime green" [[[[[['steel'], 'or', ['iron']]], 'and', 'lime green']]] not steel or iron and "lime green" [[['not', 'steel'], 'or', ['iron', 'and', 'lime green']]] not(steel or iron) and "lime green" [[['not', [[['steel'], 'or', ['iron']]], 'and', 'lime green']]] These results can now be evaluated using a depth-first recursive method, and the AND, OR, and NOT expressions will be evaluated in the proper precedence.