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_represent.py
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_represent.py
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"""Handle representations necessary for informative error messages."""
import ast
import inspect
import re
import reprlib
import textwrap
import uuid
from typing import Any, Mapping, MutableMapping, Callable, List, Dict, Iterable # pylint: disable=unused-import
from typing import Optional, Tuple # pylint: disable=unused-import
import asttokens
import icontract._recompute
from icontract._types import Contract
# pylint does not play with typing.Mapping.
# pylint: disable=unsubscriptable-object
def _representable(value: Any) -> bool:
"""
Check whether we want to represent the value in the error message on contract breach.
We do not want to represent classes, methods, modules and functions.
:param value: value related to an AST node
:return: True if we want to represent it in the violation error
"""
return not inspect.isclass(value) and not inspect.isfunction(value) and not inspect.ismethod(value) and not \
inspect.ismodule(value) and not inspect.isbuiltin(value)
class Visitor(ast.NodeVisitor):
"""Traverse the abstract syntax tree and collect the representations of the selected nodes."""
# pylint: disable=invalid-name
# pylint: disable=missing-docstring
def __init__(self, recomputed_values: Mapping[ast.AST, Any], variable_lookup: List[Mapping[str, Any]],
atok: asttokens.ASTTokens) -> None:
"""
Initialize.
:param recomputed_values: AST node of a condition function -> value associated with the node
:param variable_lookup:
list of lookup tables to look-up the values of the variables, sorted by precedence.
The visitor needs it here to check whether we overrode a built-in variable (like ``id``).
:param atok: parsed AST tree and tokens with additional positions in source code
"""
self._recomputed_values = recomputed_values
self._variable_lookup = variable_lookup
self.reprs = dict() # type: MutableMapping[str, str]
self._atok = atok
def visit_Name(self, node: ast.Name) -> None:
"""
Resolve the name from the variable look-up and the built-ins.
Due to possible branching (e.g., If-expressions), some nodes might lack the recomputed values. These nodes
are ignored.
"""
if node in self._recomputed_values:
value = self._recomputed_values[node]
# Check if it is a non-built-in
is_builtin = True
for lookup in self._variable_lookup:
if node.id in lookup:
is_builtin = False
break
if not is_builtin and _representable(value=value):
text = self._atok.get_text(node)
self.reprs[text] = value
self.generic_visit(node=node)
def visit_Attribute(self, node: ast.Attribute) -> None:
"""Represent the attribute by dumping its source code."""
if node in self._recomputed_values:
value = self._recomputed_values[node]
if _representable(value=value):
text = self._atok.get_text(node)
self.reprs[text] = value
self.generic_visit(node=node)
def visit_Call(self, node: ast.Call) -> None:
"""Represent the call by dumping its source code."""
if node in self._recomputed_values:
value = self._recomputed_values[node]
text = self._atok.get_text(node)
self.reprs[text] = value
self.generic_visit(node=node)
def visit_ListComp(self, node: ast.ListComp) -> None:
"""Represent the list comprehension by dumping its source code."""
if node in self._recomputed_values:
value = self._recomputed_values[node]
text = self._atok.get_text(node)
self.reprs[text] = value
self.generic_visit(node=node)
def visit_SetComp(self, node: ast.ListComp) -> None:
"""Represent the set comprehension by dumping its source code."""
if node in self._recomputed_values:
value = self._recomputed_values[node]
text = self._atok.get_text(node)
self.reprs[text] = value
self.generic_visit(node=node)
def visit_DictComp(self, node: ast.DictComp) -> None:
"""Represent the dictionary comprehension by dumping its source code."""
if node in self._recomputed_values:
value = self._recomputed_values[node]
text = self._atok.get_text(node)
self.reprs[text] = value
self.generic_visit(node=node)
def _is_lambda(a_function: Callable[..., Any]) -> bool:
"""
Check whether the function is a lambda function.
>>> def some_func()->bool: return True
>>> _is_lambda(some_func)
False
>>> lmbd = lambda x: x > 0
>>> _is_lambda(lmbd)
True
:param condition: condition function of a contract
:return: True if condition is defined as lambda function
"""
return a_function.__name__ == "<lambda>"
class ConditionLambdaInspection:
"""Represent the inspection of the condition function given as a lambda."""
def __init__(self, atok: asttokens.ASTTokens, node: ast.Lambda) -> None:
"""
Initialize.
:param atok: parsed AST tree and tokens with added positional properties
:param node: lambda AST node corresponding to the condition
"""
self.atok = atok
self.node = node
self.text = atok.get_text(node.body)
_DECORATOR_RE = re.compile(r'^\s*@[a-zA-Z_]')
_DEF_CLASS_RE = re.compile(r'^\s*(def |class )')
class DecoratorInspection:
"""Represent the inspection of a decorator extracted from a source file and embedded in a dummy dynamic module."""
def __init__(self, atok: asttokens.ASTTokens, node: ast.Call) -> None:
"""
Initialize.
:param atok: parsed AST tree and tokens with added positional properties
:param node: lambda AST node corresponding to the condition
"""
self.atok = atok
self.node = node
def inspect_decorator(lines: List[str], lineno: int, filename: str) -> DecoratorInspection:
"""
Parse the file in which the decorator is called and figure out the corresponding call AST node.
:param lines: lines of the source file corresponding to the decorator call
:param lineno: line index (starting with 0) of one of the lines in the decorator call
:param filename: name of the file where decorator is called
:return: inspected decorator call
"""
if lineno < 0 or lineno >= len(lines):
raise ValueError(("Given line number {} of one of the decorator lines "
"is not within the range [{}, {}) of lines in {}").format(lineno, 0, len(lines), filename))
# Go up till a line starts with a decorator
decorator_lineno = None # type: Optional[int]
for i in range(lineno, -1, -1):
if _DECORATOR_RE.match(lines[i]):
decorator_lineno = i
break
if decorator_lineno is None:
raise SyntaxError("Decorator corresponding to the line {} could not be found in file {}: {!r}".format(
lineno + 1, filename, lines[lineno]))
# Find the decorator end -- it's either a function definition, a class definition or another decorator
decorator_end_lineno = None # type: Optional[int]
for i in range(lineno + 1, len(lines)):
line = lines[i]
if _DECORATOR_RE.match(line) or _DEF_CLASS_RE.match(line):
decorator_end_lineno = i
break
if decorator_end_lineno is None:
raise SyntaxError(("The next statement following the decorator corresponding to the line {} "
"could not be found in file {}: {!r}").format(lineno + 1, filename, lines[lineno]))
decorator_lines = lines[decorator_lineno:decorator_end_lineno]
# We need to dedent the decorator and add a dummy decoratee so that we can parse its text as valid source code.
decorator_text = textwrap.dedent("".join(decorator_lines)) + "def dummy_{}(): pass".format(uuid.uuid4().hex)
atok = asttokens.ASTTokens(decorator_text, parse=True)
assert isinstance(atok.tree, ast.Module), "Expected the parsed decorator text to live in an AST module."
module_node = atok.tree
assert len(module_node.body) == 1, "Expected the module AST of the decorator text to have a single statement."
assert isinstance(module_node.body[0], ast.FunctionDef), \
"Expected the only statement in the AST module corresponding to the decorator text to be a function definition."
func_def_node = module_node.body[0]
assert len(func_def_node.decorator_list) == 1, \
"Expected the function AST node corresponding to the decorator text to have a single decorator."
assert isinstance(func_def_node.decorator_list[0], ast.Call), \
"Expected the only decorator in the function definition AST node corresponding to the decorator text " \
"to be a call node."
call_node = func_def_node.decorator_list[0]
return DecoratorInspection(atok=atok, node=call_node)
def find_lambda_condition(decorator_inspection: DecoratorInspection) -> Optional[ConditionLambdaInspection]:
"""
Inspect the decorator and extract the condition as lambda.
If the condition is not given as a lambda function, return None.
"""
call_node = decorator_inspection.node
lambda_node = None # type: Optional[ast.Lambda]
if len(call_node.args) > 0:
assert isinstance(call_node.args[0], ast.Lambda), \
("Expected the first argument to the decorator to be a condition as lambda AST node, "
"but got: {}").format(type(call_node.args[0]))
lambda_node = call_node.args[0]
elif len(call_node.keywords) > 0:
for keyword in call_node.keywords:
if keyword.arg == "condition":
assert isinstance(keyword.value, ast.Lambda), \
"Expected lambda node as value of the 'condition' argument to the decorator."
lambda_node = keyword.value
break
assert lambda_node is not None, "Expected to find a keyword AST node with 'condition' arg, but found none"
else:
raise AssertionError(
"Expected a call AST node of a decorator to have either args or keywords, but got: {}".format(
ast.dump(call_node)))
return ConditionLambdaInspection(atok=decorator_inspection.atok, node=lambda_node)
def repr_values(condition: Callable[..., bool], lambda_inspection: Optional[ConditionLambdaInspection],
condition_kwargs: Mapping[str, Any], a_repr: reprlib.Repr) -> List[str]:
# pylint: disable=too-many-locals
"""
Represent function arguments and frame values in the error message on contract breach.
:param condition: condition function of the contract
:param lambda_inspection:
inspected lambda AST node corresponding to the condition function (None if the condition was not given as a
lambda function)
:param condition_kwargs: condition arguments
:param a_repr: representation instance that defines how the values are represented.
:return: list of value representations
"""
if _is_lambda(a_function=condition):
assert lambda_inspection is not None, "Expected a lambda inspection when given a condition as a lambda function"
else:
assert lambda_inspection is None, "Expected no lambda inspection in a condition given as a non-lambda function"
reprs = dict() # type: MutableMapping[str, Any]
if lambda_inspection is not None:
# Collect the variable lookup of the condition function:
variable_lookup = [] # type: List[Mapping[str, Any]]
# Add condition arguments to the lookup
variable_lookup.append(condition_kwargs)
# Add closure to the lookup
closure_dict = dict() # type: Dict[str, Any]
if condition.__closure__ is not None: # type: ignore
closure_cells = condition.__closure__ # type: ignore
freevars = condition.__code__.co_freevars
assert len(closure_cells) == len(freevars), \
"Number of closure cells of a condition function ({}) == number of free vars ({})".format(
len(closure_cells), len(freevars))
for cell, freevar in zip(closure_cells, freevars):
closure_dict[freevar] = cell.cell_contents
variable_lookup.append(closure_dict)
# Add globals to the lookup
if condition.__globals__ is not None: # type: ignore
variable_lookup.append(condition.__globals__) # type: ignore
# pylint: disable=protected-access
recompute_visitor = icontract._recompute.Visitor(variable_lookup=variable_lookup)
recompute_visitor.visit(node=lambda_inspection.node.body)
recomputed_values = recompute_visitor.recomputed_values
repr_visitor = Visitor(
recomputed_values=recomputed_values, variable_lookup=variable_lookup, atok=lambda_inspection.atok)
repr_visitor.visit(node=lambda_inspection.node.body)
reprs = repr_visitor.reprs
else:
for key, val in condition_kwargs.items():
if _representable(value=val):
reprs[key] = val
parts = [] # type: List[str]
for key in sorted(reprs.keys()):
parts.append('{} was {}'.format(key, a_repr.repr(reprs[key])))
return parts
def generate_message(contract: Contract, condition_kwargs: Mapping[str, Any]) -> str:
"""Generate the message upon contract violation."""
# pylint: disable=protected-access
parts = [] # type: List[str]
if contract.location is not None:
parts.append("{}:\n".format(contract.location))
if contract.description is not None:
parts.append("{}: ".format(contract.description))
lambda_inspection = None # type: Optional[ConditionLambdaInspection]
if not _is_lambda(a_function=contract.condition):
condition_text = contract.condition.__name__
else:
# We need to extract the source code corresponding to the decorator since inspect.getsource() is broken with
# lambdas.
# Find the line corresponding to the condition lambda
lines, condition_lineno = inspect.findsource(contract.condition)
filename = inspect.getsourcefile(contract.condition)
assert filename is not None
decorator_inspection = inspect_decorator(lines=lines, lineno=condition_lineno, filename=filename)
lambda_inspection = find_lambda_condition(decorator_inspection=decorator_inspection)
assert lambda_inspection is not None, \
"Expected lambda_inspection to be non-None if _is_lambda is True on: {}".format(contract.condition)
condition_text = lambda_inspection.text
parts.append(condition_text)
repr_vals = repr_values(
condition=contract.condition,
lambda_inspection=lambda_inspection,
condition_kwargs=condition_kwargs,
a_repr=contract._a_repr)
if len(repr_vals) == 0:
# Do not append anything since no value could be represented as a string.
# This could appear in case we have, for example, a generator expression as the return value of a lambda.
pass
elif len(repr_vals) == 1:
parts.append(': ')
parts.append(repr_vals[0])
else:
parts.append(':\n')
parts.append('\n'.join(repr_vals))
msg = "".join(parts)
return msg