support lambda in gui builder (#1476)

* support lambda in gui builder
resolves #1379

* Fabs's comment + manage objects

* ignore mypy error

* ignore B023 Function definition does not bind loop variable `key`

* support python 3.8
Which has no unparse

* codespell

* another try

* another try

* another try

* keep things private

* Long's comments
support multiple lambdas

* Long's comment

---------

Co-authored-by: Fred Lefévère-Laoide <Fred.Lefevere-Laoide@Taipy.io>

taipy/gui/builder/_api_generator.py

@@ -120,7 +120,6 @@ class _ElementApiGenerator(object, metaclass=_Singleton):
             classname,
             (ElementBaseClass,),
             {
-                "__init__": lambda self, *args, **kwargs: ElementBaseClass.__init__(self, *args, **kwargs),
                 "_ELEMENT_NAME": element_name,
                 "_DEFAULT_PROPERTY": default_property,
             },

taipy/gui/builder/_element.py

@@ -11,14 +11,24 @@
 
 from __future__ import annotations
 
+import ast
 import copy
+import inspect
+import io
 import re
+import sys
 import typing as t
 from abc import ABC, abstractmethod
 from collections.abc import Iterable
+from types import FrameType, FunctionType
 
+from .._warnings import _warn
+
+if sys.version_info < (3, 9):
+    from ..utils.unparse import _Unparser
 from ._context_manager import _BuilderContextManager
 from ._factory import _BuilderFactory
+from ._utils import _LambdaByName, _python_builtins, _TransformVarToValue
 
 if t.TYPE_CHECKING:
     from ..gui import Gui
@@ -30,6 +40,7 @@ class _Element(ABC):
     _ELEMENT_NAME = ""
     _DEFAULT_PROPERTY = ""
     __RE_INDEXED_PROPERTY = re.compile(r"^(.*?)__([\w\d]+)$")
+    _NEW_LAMBDA_NAME = "new_lambda"
 
     def __new__(cls, *args, **kwargs):
         obj = super(_Element, cls).__new__(cls)
@@ -39,7 +50,12 @@ class _Element(ABC):
         return obj
 
     def __init__(self, *args, **kwargs) -> None:
+        self.__variables: t.Dict[str, FunctionType] = {}
         self._properties: t.Dict[str, t.Any] = {}
+        self.__calling_frame = t.cast(
+            FrameType, t.cast(FrameType, t.cast(FrameType, inspect.currentframe()).f_back).f_back
+        )
+
         if args and self._DEFAULT_PROPERTY != "":
             self._properties = {self._DEFAULT_PROPERTY: args[0]}
         self._properties.update(kwargs)
@@ -49,10 +65,10 @@ class _Element(ABC):
         self._properties.update(kwargs)
         self.parse_properties()
 
-    # Convert property value to string
+    # Convert property value to string/function
     def parse_properties(self):
         self._properties = {
-            _Element._parse_property_key(k): _Element._parse_property(v) for k, v in self._properties.items()
+            _Element._parse_property_key(k): self._parse_property(k, v) for k, v in self._properties.items()
         }
 
     # Get a deepcopy version of the properties
@@ -65,14 +81,58 @@ class _Element(ABC):
             return f"{match.group(1)}[{match.group(2)}]"
         return key
 
-    @staticmethod
-    def _parse_property(value: t.Any) -> t.Any:
+    def _parse_property(self, key: str, value: t.Any) -> t.Any:
         if isinstance(value, (str, dict, Iterable)):
             return value
+        if isinstance(value, FunctionType):
+            if key.startswith("on_"):
+                return value
+            else:
+                try:
+                    st = ast.parse(inspect.getsource(value.__code__).strip())
+                    lambda_by_name: t.Dict[str, ast.Lambda] = {}
+                    _LambdaByName(self._ELEMENT_NAME, lambda_by_name).visit(st)
+                    lambda_fn = lambda_by_name.get(
+                        key,
+                        lambda_by_name.get(_LambdaByName._DEFAULT_NAME, None)
+                        if key == self._DEFAULT_PROPERTY
+                        else None,
+                    )
+                    if lambda_fn is not None:
+                        args = [arg.arg for arg in lambda_fn.args.args]
+                        targets = [
+                            compr.target.id  # type: ignore[attr-defined]
+                            for node in ast.walk(lambda_fn.body)
+                            if isinstance(node, ast.ListComp)
+                            for compr in node.generators
+                        ]
+                        tree = _TransformVarToValue(self.__calling_frame, args + targets + _python_builtins).visit(
+                            lambda_fn
+                        )
+                        ast.fix_missing_locations(tree)
+                        if sys.version_info < (3, 9):  # python 3.8 ast has no unparse
+                            string_fd = io.StringIO()
+                            _Unparser(tree, string_fd)
+                            string_fd.seek(0)
+                            lambda_text = string_fd.read()
+                        else:
+                            lambda_text = ast.unparse(tree)
+                        new_code = compile(f"{_Element._NEW_LAMBDA_NAME} = {lambda_text}", "<ast>", "exec")
+                        namespace: t.Dict[str, FunctionType] = {}
+                        exec(new_code, namespace)
+                        var_name = f"__lambda_{id(namespace[_Element._NEW_LAMBDA_NAME])}"
+                        self.__variables[var_name] = namespace[_Element._NEW_LAMBDA_NAME]
+                        return f'{{{var_name}({", ".join(args)})}}'
+                except Exception as e:
+                    _warn("Error in lambda expression", e)
         if hasattr(value, "__name__"):
             return str(getattr(value, "__name__"))  # noqa: B009
         return str(value)
 
+    def _bind_variables(self, gui: "Gui"):
+        for var_name, var_value in self.__variables.items():
+            gui._bind_var_val(var_name, var_value)
+
     @abstractmethod
     def _render(self, gui: "Gui") -> str:
         pass
@@ -99,6 +159,7 @@ class _Block(_Element):
         _BuilderContextManager().pop()
 
     def _render(self, gui: "Gui") -> str:
+        self._bind_variables(gui)
         el = _BuilderFactory.create_element(gui, self._ELEMENT_NAME, self._deepcopy_properties())
         return f"{el[0]}{self._render_children(gui)}</{el[1]}>"
 
@@ -162,6 +223,7 @@ class html(_Block):
         self._content = args[1] if len(args) > 1 else ""
 
     def _render(self, gui: "Gui") -> str:
+        self._bind_variables(gui)
         if self._ELEMENT_NAME:
             attrs = ""
             if self._properties:
@@ -178,6 +240,7 @@ class _Control(_Element):
         super().__init__(*args, **kwargs)
 
     def _render(self, gui: "Gui") -> str:
+        self._bind_variables(gui)
         el = _BuilderFactory.create_element(gui, self._ELEMENT_NAME, self._deepcopy_properties())
         return (
             f"<div>{el[0]}</{el[1]}></div>"

taipy/gui/builder/_utils.py

@@ -0,0 +1,63 @@
+# Copyright 2021-2024 Avaiga Private Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+# an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+# specific language governing permissions and limitations under the License.
+
+from __future__ import annotations
+
+import ast
+import builtins
+import typing as t
+from operator import attrgetter
+from types import FrameType
+
+_python_builtins = dir(builtins)
+
+
+def _get_value_in_frame(frame: FrameType, name: str):
+    if not frame:
+        return None
+    if name in frame.f_locals:
+        return frame.f_locals.get(name)
+    return _get_value_in_frame(t.cast(FrameType, frame.f_back), name)
+
+
+class _TransformVarToValue(ast.NodeTransformer):
+    def __init__(self, frame: FrameType, non_vars: t.List[str]) -> None:
+        super().__init__()
+        self.frame = frame
+        self.non_vars = non_vars
+
+    def visit_Name(self, node):
+        var_parts = node.id.split(".", 2)
+        if var_parts[0] in self.non_vars:
+            return node
+        value = _get_value_in_frame(self.frame, var_parts[0])
+        if len(var_parts) > 1:
+            value = attrgetter(var_parts[1])(value)
+        return ast.Constant(value=value, kind=None)
+
+
+class _LambdaByName(ast.NodeVisitor):
+    _DEFAULT_NAME = "<default>"
+
+    def __init__(self, element_name: str, lambdas: t.Dict[str, ast.Lambda]) -> None:
+        super().__init__()
+        self.element_name = element_name
+        self.lambdas = lambdas
+
+    def visit_Call(self, node):
+        if node.func.attr == self.element_name:
+            if self.lambdas.get(_LambdaByName._DEFAULT_NAME, None) is None:
+                self.lambdas[_LambdaByName._DEFAULT_NAME] = next(
+                    (arg for arg in node.args if isinstance(arg, ast.Lambda)), None
+                )
+            for kwd in node.keywords:
+                if isinstance(kwd.value, ast.Lambda):
+                    self.lambdas[kwd.arg] = kwd.value

taipy/gui/utils/unparse.py

@@ -0,0 +1,731 @@
+# Copyright 2021-2024 Avaiga Private Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+# an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+# specific language governing permissions and limitations under the License.
+
+# from https://github.com/python/cpython/blob/3.8/Tools/parser/unparse.py to unparse an ast tree with python < 3.9
+
+import ast
+import io
+import sys
+
+# Large float and imaginary literals get turned into infinities in the AST.
+# We unparse those infinities to INFSTR.
+_INFSTR = "1e" + repr(sys.float_info.max_10_exp + 1)
+
+
+def _interleave(inter, f, seq):
+    """Call f on each item in seq, calling inter() in between."""
+    seq = iter(seq)
+    try:
+        f(next(seq))
+    except StopIteration:
+        pass
+    else:
+        for x in seq:
+            inter()
+            f(x)
+
+
+class _Unparser:
+    """Methods in this class recursively traverse an AST and
+    output source code for the abstract syntax; original formatting
+    is disregarded."""
+
+    def __init__(self, tree, file=sys.stdout):
+        """Unparser(tree, file=sys.stdout) -> None.
+        Print the source for tree to file."""
+        self.f = file
+        self._indent = 0
+        self.dispatch(tree)
+        print("", file=self.f)
+        self.f.flush()
+
+    def fill(self, text=""):
+        "Indent a piece of text, according to the current indentation level"
+        self.f.write("\n" + "    " * self._indent + text)
+
+    def write(self, text):
+        "Append a piece of text to the current line."
+        self.f.write(text)
+
+    def enter(self):
+        "Print ':', and increase the indentation."
+        self.write(":")
+        self._indent += 1
+
+    def leave(self):
+        "Decrease the indentation level."
+        self._indent -= 1
+
+    def dispatch(self, tree):
+        "Dispatcher function, dispatching tree type T to method _T."
+        if isinstance(tree, list):
+            for t in tree:
+                self.dispatch(t)
+            return
+        meth = getattr(self, "_" + tree.__class__.__name__)
+        meth(tree)
+
+    ############### Unparsing methods ######################
+    # There should be one method per concrete grammar type #
+    # Constructors should be grouped by sum type. Ideally, #
+    # this would follow the order in the grammar, but      #
+    # currently doesn't.                                   #
+    ########################################################
+
+    def _Module(self, tree):
+        for stmt in tree.body:
+            self.dispatch(stmt)
+
+    # stmt
+    def _Expr(self, tree):
+        self.fill()
+        self.dispatch(tree.value)
+
+    def _NamedExpr(self, tree):
+        self.write("(")
+        self.dispatch(tree.target)
+        self.write(" := ")
+        self.dispatch(tree.value)
+        self.write(")")
+
+    def _Import(self, t):
+        self.fill("import ")
+        _interleave(lambda: self.write(", "), self.dispatch, t.names)
+
+    def _ImportFrom(self, t):
+        self.fill("from ")
+        self.write("." * t.level)
+        if t.module:
+            self.write(t.module)
+        self.write(" import ")
+        _interleave(lambda: self.write(", "), self.dispatch, t.names)
+
+    def _Assign(self, t):
+        self.fill()
+        for target in t.targets:
+            self.dispatch(target)
+            self.write(" = ")
+        self.dispatch(t.value)
+
+    def _AugAssign(self, t):
+        self.fill()
+        self.dispatch(t.target)
+        self.write(" " + self.binop[t.op.__class__.__name__] + "= ")
+        self.dispatch(t.value)
+
+    def _AnnAssign(self, t):
+        self.fill()
+        if not t.simple and isinstance(t.target, ast.Name):
+            self.write("(")
+        self.dispatch(t.target)
+        if not t.simple and isinstance(t.target, ast.Name):
+            self.write(")")
+        self.write(": ")
+        self.dispatch(t.annotation)
+        if t.value:
+            self.write(" = ")
+            self.dispatch(t.value)
+
+    def _Return(self, t):
+        self.fill("return")
+        if t.value:
+            self.write(" ")
+            self.dispatch(t.value)
+
+    def _Pass(self, t):
+        self.fill("pass")
+
+    def _Break(self, t):
+        self.fill("break")
+
+    def _Continue(self, t):
+        self.fill("continue")
+
+    def _Delete(self, t):
+        self.fill("del ")
+        _interleave(lambda: self.write(", "), self.dispatch, t.targets)
+
+    def _Assert(self, t):
+        self.fill("assert ")
+        self.dispatch(t.test)
+        if t.msg:
+            self.write(", ")
+            self.dispatch(t.msg)
+
+    def _Global(self, t):
+        self.fill("global ")
+        _interleave(lambda: self.write(", "), self.write, t.names)
+
+    def _Nonlocal(self, t):
+        self.fill("nonlocal ")
+        _interleave(lambda: self.write(", "), self.write, t.names)
+
+    def _Await(self, t):
+        self.write("(")
+        self.write("await")
+        if t.value:
+            self.write(" ")
+            self.dispatch(t.value)
+        self.write(")")
+
+    def _Yield(self, t):
+        self.write("(")
+        self.write("yield")
+        if t.value:
+            self.write(" ")
+            self.dispatch(t.value)
+        self.write(")")
+
+    def _YieldFrom(self, t):
+        self.write("(")
+        self.write("yield from")
+        if t.value:
+            self.write(" ")
+            self.dispatch(t.value)
+        self.write(")")
+
+    def _Raise(self, t):
+        self.fill("raise")
+        if not t.exc:
+            assert not t.cause
+            return
+        self.write(" ")
+        self.dispatch(t.exc)
+        if t.cause:
+            self.write(" from ")
+            self.dispatch(t.cause)
+
+    def _Try(self, t):
+        self.fill("try")
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+        for ex in t.handlers:
+            self.dispatch(ex)
+        if t.orelse:
+            self.fill("else")
+            self.enter()
+            self.dispatch(t.orelse)
+            self.leave()
+        if t.finalbody:
+            self.fill("finally")
+            self.enter()
+            self.dispatch(t.finalbody)
+            self.leave()
+
+    def _ExceptHandler(self, t):
+        self.fill("except")
+        if t.type:
+            self.write(" ")
+            self.dispatch(t.type)
+        if t.name:
+            self.write(" as ")
+            self.write(t.name)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+
+    def _ClassDef(self, t):
+        self.write("\n")
+        for deco in t.decorator_list:
+            self.fill("@")
+            self.dispatch(deco)
+        self.fill("class " + t.name)
+        self.write("(")
+        comma = False
+        for e in t.bases:
+            if comma:
+                self.write(", ")
+            else:
+                comma = True
+            self.dispatch(e)
+        for e in t.keywords:
+            if comma:
+                self.write(", ")
+            else:
+                comma = True
+            self.dispatch(e)
+        self.write(")")
+
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+
+    def _FunctionDef(self, t):
+        self.__FunctionDef_helper(t, "def")
+
+    def _AsyncFunctionDef(self, t):
+        self.__FunctionDef_helper(t, "async def")
+
+    def __FunctionDef_helper(self, t, fill_suffix):
+        self.write("\n")
+        for deco in t.decorator_list:
+            self.fill("@")
+            self.dispatch(deco)
+        def_str = fill_suffix + " " + t.name + "("
+        self.fill(def_str)
+        self.dispatch(t.args)
+        self.write(")")
+        if t.returns:
+            self.write(" -> ")
+            self.dispatch(t.returns)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+
+    def _For(self, t):
+        self.__For_helper("for ", t)
+
+    def _AsyncFor(self, t):
+        self.__For_helper("async for ", t)
+
+    def __For_helper(self, fill, t):
+        self.fill(fill)
+        self.dispatch(t.target)
+        self.write(" in ")
+        self.dispatch(t.iter)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+        if t.orelse:
+            self.fill("else")
+            self.enter()
+            self.dispatch(t.orelse)
+            self.leave()
+
+    def _If(self, t):
+        self.fill("if ")
+        self.dispatch(t.test)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+        # collapse nested ifs into equivalent elifs.
+        while t.orelse and len(t.orelse) == 1 and isinstance(t.orelse[0], ast.If):
+            t = t.orelse[0]
+            self.fill("elif ")
+            self.dispatch(t.test)
+            self.enter()
+            self.dispatch(t.body)
+            self.leave()
+        # final else
+        if t.orelse:
+            self.fill("else")
+            self.enter()
+            self.dispatch(t.orelse)
+            self.leave()
+
+    def _While(self, t):
+        self.fill("while ")
+        self.dispatch(t.test)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+        if t.orelse:
+            self.fill("else")
+            self.enter()
+            self.dispatch(t.orelse)
+            self.leave()
+
+    def _With(self, t):
+        self.fill("with ")
+        _interleave(lambda: self.write(", "), self.dispatch, t.items)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+
+    def _AsyncWith(self, t):
+        self.fill("async with ")
+        _interleave(lambda: self.write(", "), self.dispatch, t.items)
+        self.enter()
+        self.dispatch(t.body)
+        self.leave()
+
+    # expr
+    def _JoinedStr(self, t):
+        self.write("f")
+        string = io.StringIO()
+        self._fstring_JoinedStr(t, string.write)
+        self.write(repr(string.getvalue()))
+
+    def _FormattedValue(self, t):
+        self.write("f")
+        string = io.StringIO()
+        self._fstring_FormattedValue(t, string.write)
+        self.write(repr(string.getvalue()))
+
+    def _fstring_JoinedStr(self, t, write):
+        for value in t.values:
+            meth = getattr(self, "_fstring_" + type(value).__name__)
+            meth(value, write)
+
+    def _fstring_Constant(self, t, write):
+        assert isinstance(t.value, str)
+        value = t.value.replace("{", "{{").replace("}", "}}")
+        write(value)
+
+    def _fstring_FormattedValue(self, t, write):
+        write("{")
+        expr = io.StringIO()
+        _Unparser(t.value, expr)
+        expr = expr.getvalue().rstrip("\n")
+        if expr.startswith("{"):
+            write(" ")  # Separate pair of opening brackets as "{ {"
+        write(expr)
+        if t.conversion != -1:
+            conversion = chr(t.conversion)
+            assert conversion in "sra"
+            write(f"!{conversion}")
+        if t.format_spec:
+            write(":")
+            meth = getattr(self, "_fstring_" + type(t.format_spec).__name__)
+            meth(t.format_spec, write)
+        write("}")
+
+    def _Name(self, t):
+        self.write(t.id)
+
+    def _write_constant(self, value):
+        if isinstance(value, (float, complex)):
+            # Substitute overflowing decimal literal for AST infinities.
+            self.write(repr(value).replace("inf", _INFSTR))
+        else:
+            self.write(repr(value))
+
+    def _Constant(self, t):
+        value = t.value
+        if isinstance(value, tuple):
+            self.write("(")
+            if len(value) == 1:
+                self._write_constant(value[0])
+                self.write(",")
+            else:
+                _interleave(lambda: self.write(", "), self._write_constant, value)
+            self.write(")")
+        elif value is ...:
+            self.write("...")
+        else:
+            if t.kind == "u":
+                self.write("u")
+            self._write_constant(t.value)
+
+    def _List(self, t):
+        self.write("[")
+        _interleave(lambda: self.write(", "), self.dispatch, t.elts)
+        self.write("]")
+
+    def _ListComp(self, t):
+        self.write("[")
+        self.dispatch(t.elt)
+        for gen in t.generators:
+            self.dispatch(gen)
+        self.write("]")
+
+    def _GeneratorExp(self, t):
+        self.write("(")
+        self.dispatch(t.elt)
+        for gen in t.generators:
+            self.dispatch(gen)
+        self.write(")")
+
+    def _SetComp(self, t):
+        self.write("{")
+        self.dispatch(t.elt)
+        for gen in t.generators:
+            self.dispatch(gen)
+        self.write("}")
+
+    def _DictComp(self, t):
+        self.write("{")
+        self.dispatch(t.key)
+        self.write(": ")
+        self.dispatch(t.value)
+        for gen in t.generators:
+            self.dispatch(gen)
+        self.write("}")
+
+    def _comprehension(self, t):
+        if t.is_async:
+            self.write(" async for ")
+        else:
+            self.write(" for ")
+        self.dispatch(t.target)
+        self.write(" in ")
+        self.dispatch(t.iter)
+        for if_clause in t.ifs:
+            self.write(" if ")
+            self.dispatch(if_clause)
+
+    def _IfExp(self, t):
+        self.write("(")
+        self.dispatch(t.body)
+        self.write(" if ")
+        self.dispatch(t.test)
+        self.write(" else ")
+        self.dispatch(t.orelse)
+        self.write(")")
+
+    def _Set(self, t):
+        assert t.elts  # should be at least one element
+        self.write("{")
+        _interleave(lambda: self.write(", "), self.dispatch, t.elts)
+        self.write("}")
+
+    def _Dict(self, t):
+        self.write("{")
+
+        def write_key_value_pair(k, v):
+            self.dispatch(k)
+            self.write(": ")
+            self.dispatch(v)
+
+        def write_item(item):
+            k, v = item
+            if k is None:
+                # for dictionary unpacking operator in dicts {**{'y': 2}}
+                # see PEP 448 for details
+                self.write("**")
+                self.dispatch(v)
+            else:
+                write_key_value_pair(k, v)
+
+        _interleave(lambda: self.write(", "), write_item, zip(t.keys, t.values))
+        self.write("}")
+
+    def _Tuple(self, t):
+        self.write("(")
+        if len(t.elts) == 1:
+            elt = t.elts[0]
+            self.dispatch(elt)
+            self.write(",")
+        else:
+            _interleave(lambda: self.write(", "), self.dispatch, t.elts)
+        self.write(")")
+
+    unop = {"Invert": "~", "Not": "not", "UAdd": "+", "USub": "-"}
+
+    def _UnaryOp(self, t):
+        self.write("(")
+        self.write(self.unop[t.op.__class__.__name__])
+        self.write(" ")
+        self.dispatch(t.operand)
+        self.write(")")
+
+    binop = {
+        "Add": "+",
+        "Sub": "-",
+        "Mult": "*",
+        "MatMult": "@",
+        "Div": "/",
+        "Mod": "%",
+        "LShift": "<<",
+        "RShift": ">>",
+        "BitOr": "|",
+        "BitXor": "^",
+        "BitAnd": "&",
+        "FloorDiv": "//",
+        "Pow": "**",
+    }
+
+    def _BinOp(self, t):
+        self.write("(")
+        self.dispatch(t.left)
+        self.write(" " + self.binop[t.op.__class__.__name__] + " ")
+        self.dispatch(t.right)
+        self.write(")")
+
+    cmpops = {
+        "Eq": "==",
+        "NotEq": "!=",
+        "Lt": "<",
+        "LtE": "<=",
+        "Gt": ">",
+        "GtE": ">=",
+        "Is": "is",
+        "IsNot": "is not",
+        "In": "in",
+        "NotIn": "not in",  # codespell:ignore
+    }
+
+    def _Compare(self, t):
+        self.write("(")
+        self.dispatch(t.left)
+        for o, e in zip(t.ops, t.comparators):
+            self.write(" " + self.cmpops[o.__class__.__name__] + " ")
+            self.dispatch(e)
+        self.write(")")
+
+    boolops = {ast.And: "and", ast.Or: "or"}
+
+    def _BoolOp(self, t):
+        self.write("(")
+        s = " %s " % self.boolops[t.op.__class__]
+        _interleave(lambda: self.write(s), self.dispatch, t.values)
+        self.write(")")
+
+    def _Attribute(self, t):
+        self.dispatch(t.value)
+        # Special case: 3.__abs__() is a syntax error, so if t.value
+        # is an integer literal then we need to either parenthesize
+        # it or add an extra space to get 3 .__abs__().
+        if isinstance(t.value, ast.Constant) and isinstance(t.value.value, int):
+            self.write(" ")
+        self.write(".")
+        self.write(t.attr)
+
+    def _Call(self, t):
+        self.dispatch(t.func)
+        self.write("(")
+        comma = False
+        for e in t.args:
+            if comma:
+                self.write(", ")
+            else:
+                comma = True
+            self.dispatch(e)
+        for e in t.keywords:
+            if comma:
+                self.write(", ")
+            else:
+                comma = True
+            self.dispatch(e)
+        self.write(")")
+
+    def _Subscript(self, t):
+        self.dispatch(t.value)
+        self.write("[")
+        if isinstance(t.slice, ast.Index) and isinstance(t.slice.value, ast.Tuple) and t.slice.value.elts:
+            if len(t.slice.value.elts) == 1:
+                elt = t.slice.value.elts[0]
+                self.dispatch(elt)
+                self.write(",")
+            else:
+                _interleave(lambda: self.write(", "), self.dispatch, t.slice.value.elts)
+        else:
+            self.dispatch(t.slice)
+        self.write("]")
+
+    def _Starred(self, t):
+        self.write("*")
+        self.dispatch(t.value)
+
+    # slice
+    def _Ellipsis(self, t):
+        self.write("...")
+
+    def _Index(self, t):
+        self.dispatch(t.value)
+
+    def _Slice(self, t):
+        if t.lower:
+            self.dispatch(t.lower)
+        self.write(":")
+        if t.upper:
+            self.dispatch(t.upper)
+        if t.step:
+            self.write(":")
+            self.dispatch(t.step)
+
+    def _ExtSlice(self, t):
+        if len(t.dims) == 1:
+            elt = t.dims[0]
+            self.dispatch(elt)
+            self.write(",")
+        else:
+            _interleave(lambda: self.write(", "), self.dispatch, t.dims)
+
+    # argument
+    def _arg(self, t):
+        self.write(t.arg)
+        if t.annotation:
+            self.write(": ")
+            self.dispatch(t.annotation)
+
+    # others
+    def _arguments(self, t):
+        first = True
+        # normal arguments
+        all_args = t.posonlyargs + t.args
+        defaults = [None] * (len(all_args) - len(t.defaults)) + t.defaults
+        for index, elements in enumerate(zip(all_args, defaults), 1):
+            a, d = elements
+            if first:
+                first = False
+            else:
+                self.write(", ")
+            self.dispatch(a)
+            if d:
+                self.write("=")
+                self.dispatch(d)
+            if index == len(t.posonlyargs):
+                self.write(", /")
+
+        # varargs, or bare '*' if no varargs but keyword-only arguments present
+        if t.vararg or t.kwonlyargs:
+            if first:
+                first = False
+            else:
+                self.write(", ")
+            self.write("*")
+            if t.vararg:
+                self.write(t.vararg.arg)
+                if t.vararg.annotation:
+                    self.write(": ")
+                    self.dispatch(t.vararg.annotation)
+
+        # keyword-only arguments
+        if t.kwonlyargs:
+            for a, d in zip(t.kwonlyargs, t.kw_defaults):
+                if first:
+                    first = False
+                else:
+                    self.write(", ")
+                (self.dispatch(a),)
+                if d:
+                    self.write("=")
+                    self.dispatch(d)
+
+        # kwargs
+        if t.kwarg:
+            if first:
+                first = False
+            else:
+                self.write(", ")
+            self.write("**" + t.kwarg.arg)
+            if t.kwarg.annotation:
+                self.write(": ")
+                self.dispatch(t.kwarg.annotation)
+
+    def _keyword(self, t):
+        if t.arg is None:
+            self.write("**")
+        else:
+            self.write(t.arg)
+            self.write("=")
+        self.dispatch(t.value)
+
+    def _Lambda(self, t):
+        self.write("(")
+        self.write("lambda ")
+        self.dispatch(t.args)
+        self.write(": ")
+        self.dispatch(t.body)
+        self.write(")")
+
+    def _alias(self, t):
+        self.write(t.name)
+        if t.asname:
+            self.write(" as " + t.asname)
+
+    def _withitem(self, t):
+        self.dispatch(t.context_expr)
+        if t.optional_vars:
+            self.write(" as ")
+            self.dispatch(t.optional_vars)

tests/gui/builder/test_lambda.py

@@ -0,0 +1,33 @@
+# Copyright 2021-2024 Avaiga Private Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+# an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+# specific language governing permissions and limitations under the License.
+
+import taipy.gui.builder as tgb
+from taipy.gui import Gui
+
+
+def test_builder_lambda(gui: Gui, test_client, helpers):
+    message = {"a": "value A", "b": "value B"}
+    gui._bind_var_val("message", message)
+    with tgb.Page(frame=None) as page:
+        for key in message:
+            tgb.text(lambda message: str(message.get(key)))  # type: ignore[attr-defined] # noqa: B023
+    expected_list = ['defaultValue="value A"', 'defaultValue="value B"']
+    helpers.test_control_builder(gui, page, expected_list)
+
+
+def test_builder_lambda_2(gui: Gui, test_client, helpers):
+    message = {"a": "value A", "b": "value B"}
+    gui._bind_var_val("message", message)
+    with tgb.Page(frame=None) as page:
+        for key in message:
+            tgb.text(lambda message: str(message.get(key)), mode=lambda message: "mode " + str(message.get(key)))  # type: ignore[attr-defined] # noqa: B023
+    expected_list = ['defaultValue="value A"', 'defaultValue="value B"', 'mode="mode value A"', 'mode="mode value B"']
+    helpers.test_control_builder(gui, page, expected_list)