From 270ba6887febd4d29cc91071b60acf4ed4c6392d Mon Sep 17 00:00:00 2001 From: krasimir Date: Wed, 15 Jul 2015 12:12:50 +0000 Subject: [PATCH] add the Python API tutorial to the GF home page --- doc/python-api.html | 433 ++++++++++++++++++++++++++++++++++++++++++++ index.html | 3 +- 2 files changed, 435 insertions(+), 1 deletion(-) create mode 100644 doc/python-api.html diff --git a/doc/python-api.html b/doc/python-api.html new file mode 100644 index 000000000..01ce87e90 --- /dev/null +++ b/doc/python-api.html @@ -0,0 +1,433 @@ + + + + + +

Using the Python binding to the C runtime

+

Krasimir Angelov, July 2015

+ +

Loading the Grammar

+ +Before you use the Python binding you need to import the pgf module. +
+>>> import pgf
+
+ +Once you have the module imported, you can use the dir and +help functions to see what kind of functionality is available. +dir takes an object and returns a list of methods available +in the object: +
+>>> dir(pgf)
+
+help is a little bit more advanced and it tries +to produce more human readable documentation, which more over +contains comments: +
+>>> help(pgf)
+
+ +A grammar is loaded by calling the method readPGF: +
+>>> gr = pgf.readPGF("App12.pgf")
+
+ +From the grammar you can query the set of available languages. +It is accessible through the property languages which +is a map from language name to an object of class pgf.Concr +which respresents the language. +For example the following will extract the English language: +
+>>> eng = gr.languages["AppEng"]
+>>> print eng
+<pgf.Concr object at 0x7f7dfa4471d0>
+
+ +

Parsing

+ +All language specific services are available as methods of the +class pgf.Concr. For example to invoke the parser, you +can call: +
+>>> i = eng.parse("this is a small theatre")
+
+This gives you an iterator which can enumerates all possible +abstract trees. You can get the next tree by calling next: +
+>>> p,e = i.next()
+
+The results are always pairs of probability and tree. The probabilities +are negated logarithmic probabilities and which means that the lowest +number encodes the most probable result. The possible trees are +returned in decreasing probability order (i.e. increasing negated logarithm). +The first tree should have the smallest p: +
+>>> print p
+35.9166526794
+
+and this is the corresponding abstract tree: +
+>>> print e
+PhrUtt NoPConj (UttS (UseCl (TTAnt TPres ASimul) PPos (PredVP (DetNP (DetQuant this_Quant NumSg)) (UseComp (CompNP (DetCN (DetQuant IndefArt NumSg) (AdjCN (PositA small_A) (UseN theatre_N)))))))) NoVoc
+
+ +The parse method has also the following optional parameters: + + + + + +
catstart category
nmaximum number of trees
heuristicsa real number from 0 to 1
callbacksa list of category and callback function
+ +By using these parameters it is possible for instance to change the start category for +the parser or to limit the number of trees returned from the parser. For example +parsing with a different start category can be done as follows: +
+>>> i = eng.parse("a small theatre", cat="NP")
+
+ +

The heuristics factor can be used to trade parsing speed for quality. +By default the list of trees is sorted by probability this corresponds +to factor 0.0. When we increase the factor then parsing becomes faster +but at the same time the sorting becomes imprecise. The worst +factor is 1.0. In any case the parser always returns the same set of +trees but in different order. Our experience is that even a factor +of about 0.6-0.8 with the translation grammar, still orders +the most probable tree on top of the list but further down the list +the trees become shuffled. +

+ +

+The callbacks is a list of functions that can be used for recognizing +literals. For example we use those for recognizing names and unknown +words in the translator. +

+ +

Linearization

+ +You can either linearize the result from the parser back to another +language, or you can explicitly construct a tree and then +linearize it in any language. For example, we can create +a new expression like this: +
+>>> e = pgf.readExpr("AdjCN (PositA red_A) (UseN theatre_N)")
+
+and then we can linearize it: +
+>>> print eng.linearize(e)
+red theatre
+
+This method produces only a single linearization. If you use variants +in the grammar then you might want to see all possible linearizations. +For that purpouse you should use linearizeAll: +
+>>> for s in eng.linearizeAll(e):
+       print s
+red theatre
+red theater
+
+If, instead, you need an inflection table with all possible forms +then the right method to use is tabularLinearize: +
+>>> eng.tabularLinearize(e):
+{'s Sg Nom': 'red theatre', 's Pl Nom': 'red theatres', 's Pl Gen': "red theatres'", 's Sg Gen': "red theatre's"}
+
+ +

+Finally, you could also get a linearization which is bracketed into +a list of phrases: +

+>>> [b] = eng.bracketedLinearize(e)
+>>> print b
+(CN:4 (AP:1 (A:0 red)) (CN:3 (N:2 theatre)))
+
+Each bracket is actually an object of type pgf.Bracket. The property +cat of the object gives you the name of the category and +the property children gives you a list of nested brackets. +If a phrase is discontinuous then it is represented as more than +one brackets with the same category name. In that case, the index +that you see in the example above will have the same value for all +brackets of the same phrase. +

+ +The linearization works even if there are functions in the tree +that doesn't have linearization definitions. In that case you +will just see the name of the function in the generated string. +It is sometimes helpful to be able to see whether a function +is linearizable or not. This can be done in this way: +
+>>> print eng.hasLinearization("apple_N")
+
+ +

Analysing and Constructing Expressions

+ +

+An already constructed tree can be analyzed and transformed +in the host application. For example you can deconstruct +a tree into a function name and a list of arguments: +

+>>> e.unpack()
+('AdjCN', [<pgf.Expr object at 0x7f7df6db78c8>, <pgf.Expr object at 0x7f7df6db7878>])
+
+ +The result from unpack can be different depending on the form of the +tree. If the tree is a function application then you always get +a tuple of function name and a list of arguments. If instead the +tree is just a literal string then the return value is the actual +literal. For example the result from: +
+>>> pgf.readExpr('"literal"').unpack()
+'literal'
+
+is just the string 'literal'. Situations like this can be detected +in Python by checking the type of the result from unpack. +

+ +

+For more complex analyses you can use the visitor pattern. +In object oriented languages this is just a clumpsy way to do +what is called pattern matching in most functional languages. +You need to define a class which has one method for each function +in the abstract syntax of the grammar. If the functions is called +f then you need a method called on_f. The method +will be called each time when the corresponding function is encountered, +and its arguments will be the arguments from the original tree. +If there is no matching method name then the runtime will +to call the method default. The following is an example: +

+>>> class ExampleVisitor:
+		def on_DetCN(self,quant,cn):
+			print "Found DetCN"
+			cn.visit(self)
+			
+		def on_AdjCN(self,adj,cn):
+			print "Found AdjCN"
+			cn.visit(self)
+			
+		def default(self,e):
+			pass
+>>> e2.visit(ExampleVisitor())
+Found DetCN
+Found AdjCN
+
+Here we call the method visit from the tree e2 and we give +it, as parameter, an instance of class ExampleVisitor. +ExampleVisitor has two methods on_DetCN +and on_AdjCN which are called when the top function of +the current tree is DetCN or AdjCN +correspondingly. In this example we just print a message and +we call visit recursively to go deeper into the tree. +

+ +Constructing new trees is also easy. You can either use +readExpr to read trees from strings, or you can +construct new trees from existing pieces. This is possible by +using the constructor for pgf.Expr: +
+>>> quant = pgf.readExpr("DetQuant IndefArt NumSg")
+>>> e2 = pgf.Expr("DetCN", [quant, e])
+>>> print e2
+DetCN (DetQuant IndefArt NumSg) (AdjCN (PositA red_A) (UseN theatre_N))
+
+ +

Embedded GF Grammars

+ +The GF compiler allows for easy integration of grammars in Haskell +applications. For that purpose the compiler generates Haskell code +that makes the integration of grammars easier. Since Python is a +dynamic language the same can be done at runtime. Once you load +the grammar you can call the method embed, which will +dynamically create a Python module with one Python function +for every function in the abstract syntax of the grammar. +After that you can simply import the module: +
+>>> gr.embed("App")
+<module 'App' (built-in)>
+>>> import App
+
+Now creating new trees is just a matter of calling ordinary Python +functions: +
+>>> print App.DetCN(quant,e)
+DetCN (DetQuant IndefArt NumSg) (AdjCN (PositA red_A) (UseN house_N))
+
+ +

Access the Morphological Lexicon

+ +There are two methods that gives you direct access to the morphological +lexicon. The first makes it possible to dump the full form lexicon. +The following code just iterates over the lexicon and prints each +word form with its possible analyses: +
+for entry in eng.fullFormLexicon():
+	print entry
+
+The second one implements a simple lookup. The argument is a word +form and the result is a list of analyses: +
+print eng.lookupMorpho("letter")
+[('letter_1_N', 's Sg Nom', inf), ('letter_2_N', 's Sg Nom', inf)]
+
+ +

Access the Abstract Syntax

+ +There is a simple API for accessing the abstract syntax. For example, +you can get a list of abstract functions: +
+>>> gr.functions
+....
+
+or a list of categories: +
+>>> gr.categories
+....
+
+You can also access all functions with the same result category: +
+>>> gr.functionsByCat("Weekday")
+['friday_Weekday', 'monday_Weekday', 'saturday_Weekday', 'sunday_Weekday', 'thursday_Weekday', 'tuesday_Weekday', 'wednesday_Weekday']
+
+The full type of a function can be retrieved as: +
+>>> print gr.functionType("DetCN")
+Det -> CN -> NP
+
+ +

Type Checking Abstract Trees

+ +

The runtime type checker can do type checking and type inference +for simple types. Dependent types are still not fully implemented +in the current runtime. The inference is done with method inferExpr: +

+>>> e,ty = gr.inferExpr(e)
+>>> print e
+AdjCN (PositA red_A) (UseN theatre_N)
+>>> print ty
+CN
+
+The result is a potentially updated expression and its type. In this +case we always deal with simple types, which means that the new +expression will be always equal to the original expression. However, this +wouldn't be true when dependent types are added. +

+ +

Type checking is also trivial: +

+>>> e = gr.checkExpr(e,pgf.readType("CN"))
+>>> print e
+AdjCN (PositA red_A) (UseN theatre_N)
+
+In case of type error you will get an exception: +
+>>> e = gr.checkExpr(e,pgf.readType("A"))
+pgf.TypeError: The expected type of the expression AdjCN (PositA red_A) (UseN theatre_N) is A but CN is infered
+
+

+ +

Partial Grammar Loading

+ +By default the whole grammar is compiled into a single file +which consists of an abstract syntax together will all concrete +languages. For large grammars with many languages this might be +inconvinient because loading becomes slower and the grammar takes +more memory. For that purpose you could split the grammar into +one file for the abstract syntax and one file for every concrete syntax. +This is done by using the option -split-pgf in the compiler: +
+$ gf -make -split-pgf App12.pgf
+
+ +Now you can load the grammar as usual but this time only the +abstract syntax will be loaded. You can still use the languages +property to get the list of languages and the corresponding +concrete syntax objects: +
+>>> gr = pgf.readPGF("App.pgf")
+>>> eng = gr.languages["AppEng"]
+
+However, if you now try to use the concrete syntax then you will +get an exception: +
+>>> gr.languages["AppEng"].lookupMorpho("letter")
+Traceback (most recent call last):
+  File "", line 1, in 
+pgf.PGFError: The concrete syntax is not loaded
+
+ +Before using the concrete syntax, you need to explicitly load it: +
+>>> eng.load("AppEng.pgf_c")
+>>> print eng.lookupMorpho("letter")
+[('letter_1_N', 's Sg Nom', inf), ('letter_2_N', 's Sg Nom', inf)]
+
+ +When you don't need the language anymore then you can simply +unload it: +
+>>> eng.unload()
+
+ +

GraphViz

+ +GraphViz is used for visualizing abstract syntax trees and parse trees. +In both cases the result is a GraphViz code that can be used for +rendering the trees. See the examples bellow. + +
+>>> print gr.graphvizAbstractTree(e)
+graph {
+n0[label = "AdjCN", style = "solid", shape = "plaintext"]
+n1[label = "PositA", style = "solid", shape = "plaintext"]
+n2[label = "red_A", style = "solid", shape = "plaintext"]
+n1 -- n2 [style = "solid"]
+n0 -- n1 [style = "solid"]
+n3[label = "UseN", style = "solid", shape = "plaintext"]
+n4[label = "theatre_N", style = "solid", shape = "plaintext"]
+n3 -- n4 [style = "solid"]
+n0 -- n3 [style = "solid"]
+}
+
+ +
+>>> print eng.graphvizParseTree(e)
+graph {
+  node[shape=plaintext]
+
+  subgraph {rank=same;
+    n4[label="CN"]
+  }
+
+  subgraph {rank=same;
+    edge[style=invis]
+    n1[label="AP"]
+    n3[label="CN"]
+    n1 -- n3
+  }
+  n4 -- n1
+  n4 -- n3
+
+  subgraph {rank=same;
+    edge[style=invis]
+    n0[label="A"]
+    n2[label="N"]
+    n0 -- n2
+  }
+  n1 -- n0
+  n3 -- n2
+
+  subgraph {rank=same;
+    edge[style=invis]
+    n100000[label="red"]
+    n100001[label="theatre"]
+    n100000 -- n100001
+  }
+  n0 -- n100000
+  n2 -- n100001
+}
+
+ + + + diff --git a/index.html b/index.html index 7bf14c9e6..57e65713f 100644 --- a/index.html +++ b/index.html @@ -81,7 +81,8 @@ function sitesearch() {

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