# Source code for _pytest.python_api

```
import inspect
import math
import pprint
from collections.abc import Iterable
from collections.abc import Mapping
from collections.abc import Sized
from decimal import Decimal
from itertools import filterfalse
from numbers import Number
from types import TracebackType
from typing import Any
from typing import Callable
from typing import cast
from typing import Generic
from typing import Optional
from typing import Pattern
from typing import Tuple
from typing import TypeVar
from typing import Union
from more_itertools.more import always_iterable
import _pytest._code
from _pytest.compat import overload
from _pytest.compat import STRING_TYPES
from _pytest.outcomes import fail
if False: # TYPE_CHECKING
from typing import Type # noqa: F401 (used in type string)
BASE_TYPE = (type, STRING_TYPES)
def _non_numeric_type_error(value, at):
at_str = " at {}".format(at) if at else ""
return TypeError(
"cannot make approximate comparisons to non-numeric values: {!r} {}".format(
value, at_str
)
)
# builtin pytest.approx helper
class ApproxBase:
"""
Provide shared utilities for making approximate comparisons between numbers
or sequences of numbers.
"""
# Tell numpy to use our `__eq__` operator instead of its.
__array_ufunc__ = None
__array_priority__ = 100
def __init__(self, expected, rel=None, abs=None, nan_ok=False):
__tracebackhide__ = True
self.expected = expected
self.abs = abs
self.rel = rel
self.nan_ok = nan_ok
self._check_type()
def __repr__(self):
raise NotImplementedError
def __eq__(self, actual):
return all(
a == self._approx_scalar(x) for a, x in self._yield_comparisons(actual)
)
# Ignore type because of https://github.com/python/mypy/issues/4266.
__hash__ = None # type: ignore
def __ne__(self, actual):
return not (actual == self)
def _approx_scalar(self, x):
return ApproxScalar(x, rel=self.rel, abs=self.abs, nan_ok=self.nan_ok)
def _yield_comparisons(self, actual):
"""
Yield all the pairs of numbers to be compared. This is used to
implement the `__eq__` method.
"""
raise NotImplementedError
def _check_type(self):
"""
Raise a TypeError if the expected value is not a valid type.
"""
# This is only a concern if the expected value is a sequence. In every
# other case, the approx() function ensures that the expected value has
# a numeric type. For this reason, the default is to do nothing. The
# classes that deal with sequences should reimplement this method to
# raise if there are any non-numeric elements in the sequence.
pass
def _recursive_list_map(f, x):
if isinstance(x, list):
return list(_recursive_list_map(f, xi) for xi in x)
else:
return f(x)
class ApproxNumpy(ApproxBase):
"""
Perform approximate comparisons where the expected value is numpy array.
"""
def __repr__(self):
list_scalars = _recursive_list_map(self._approx_scalar, self.expected.tolist())
return "approx({!r})".format(list_scalars)
def __eq__(self, actual):
import numpy as np
# self.expected is supposed to always be an array here
if not np.isscalar(actual):
try:
actual = np.asarray(actual)
except: # noqa
raise TypeError("cannot compare '{}' to numpy.ndarray".format(actual))
if not np.isscalar(actual) and actual.shape != self.expected.shape:
return False
return ApproxBase.__eq__(self, actual)
def _yield_comparisons(self, actual):
import numpy as np
# `actual` can either be a numpy array or a scalar, it is treated in
# `__eq__` before being passed to `ApproxBase.__eq__`, which is the
# only method that calls this one.
if np.isscalar(actual):
for i in np.ndindex(self.expected.shape):
yield actual, self.expected[i].item()
else:
for i in np.ndindex(self.expected.shape):
yield actual[i].item(), self.expected[i].item()
class ApproxMapping(ApproxBase):
"""
Perform approximate comparisons where the expected value is a mapping with
numeric values (the keys can be anything).
"""
def __repr__(self):
return "approx({!r})".format(
{k: self._approx_scalar(v) for k, v in self.expected.items()}
)
def __eq__(self, actual):
if set(actual.keys()) != set(self.expected.keys()):
return False
return ApproxBase.__eq__(self, actual)
def _yield_comparisons(self, actual):
for k in self.expected.keys():
yield actual[k], self.expected[k]
def _check_type(self):
__tracebackhide__ = True
for key, value in self.expected.items():
if isinstance(value, type(self.expected)):
msg = "pytest.approx() does not support nested dictionaries: key={!r} value={!r}\n full mapping={}"
raise TypeError(msg.format(key, value, pprint.pformat(self.expected)))
elif not isinstance(value, Number):
raise _non_numeric_type_error(self.expected, at="key={!r}".format(key))
class ApproxSequencelike(ApproxBase):
"""
Perform approximate comparisons where the expected value is a sequence of
numbers.
"""
def __repr__(self):
seq_type = type(self.expected)
if seq_type not in (tuple, list, set):
seq_type = list
return "approx({!r})".format(
seq_type(self._approx_scalar(x) for x in self.expected)
)
def __eq__(self, actual):
if len(actual) != len(self.expected):
return False
return ApproxBase.__eq__(self, actual)
def _yield_comparisons(self, actual):
return zip(actual, self.expected)
def _check_type(self):
__tracebackhide__ = True
for index, x in enumerate(self.expected):
if isinstance(x, type(self.expected)):
msg = "pytest.approx() does not support nested data structures: {!r} at index {}\n full sequence: {}"
raise TypeError(msg.format(x, index, pprint.pformat(self.expected)))
elif not isinstance(x, Number):
raise _non_numeric_type_error(
self.expected, at="index {}".format(index)
)
class ApproxScalar(ApproxBase):
"""
Perform approximate comparisons where the expected value is a single number.
"""
# Using Real should be better than this Union, but not possible yet:
# https://github.com/python/typeshed/pull/3108
DEFAULT_ABSOLUTE_TOLERANCE = 1e-12 # type: Union[float, Decimal]
DEFAULT_RELATIVE_TOLERANCE = 1e-6 # type: Union[float, Decimal]
def __repr__(self):
"""
Return a string communicating both the expected value and the tolerance
for the comparison being made, e.g. '1.0 +- 1e-6'. Use the unicode
plus/minus symbol if this is python3 (it's too hard to get right for
python2).
"""
if isinstance(self.expected, complex):
return str(self.expected)
# Infinities aren't compared using tolerances, so don't show a
# tolerance.
if math.isinf(self.expected):
return str(self.expected)
# If a sensible tolerance can't be calculated, self.tolerance will
# raise a ValueError. In this case, display '???'.
try:
vetted_tolerance = "{:.1e}".format(self.tolerance)
except ValueError:
vetted_tolerance = "???"
return "{} \u00b1 {}".format(self.expected, vetted_tolerance)
def __eq__(self, actual):
"""
Return true if the given value is equal to the expected value within
the pre-specified tolerance.
"""
if _is_numpy_array(actual):
# Call ``__eq__()`` manually to prevent infinite-recursion with
# numpy<1.13. See #3748.
return all(self.__eq__(a) for a in actual.flat)
# Short-circuit exact equality.
if actual == self.expected:
return True
# Allow the user to control whether NaNs are considered equal to each
# other or not. The abs() calls are for compatibility with complex
# numbers.
if math.isnan(abs(self.expected)):
return self.nan_ok and math.isnan(abs(actual))
# Infinity shouldn't be approximately equal to anything but itself, but
# if there's a relative tolerance, it will be infinite and infinity
# will seem approximately equal to everything. The equal-to-itself
# case would have been short circuited above, so here we can just
# return false if the expected value is infinite. The abs() call is
# for compatibility with complex numbers.
if math.isinf(abs(self.expected)):
return False
# Return true if the two numbers are within the tolerance.
return abs(self.expected - actual) <= self.tolerance
# Ignore type because of https://github.com/python/mypy/issues/4266.
__hash__ = None # type: ignore
@property
def tolerance(self):
"""
Return the tolerance for the comparison. This could be either an
absolute tolerance or a relative tolerance, depending on what the user
specified or which would be larger.
"""
def set_default(x, default):
return x if x is not None else default
# Figure out what the absolute tolerance should be. ``self.abs`` is
# either None or a value specified by the user.
absolute_tolerance = set_default(self.abs, self.DEFAULT_ABSOLUTE_TOLERANCE)
if absolute_tolerance < 0:
raise ValueError(
"absolute tolerance can't be negative: {}".format(absolute_tolerance)
)
if math.isnan(absolute_tolerance):
raise ValueError("absolute tolerance can't be NaN.")
# If the user specified an absolute tolerance but not a relative one,
# just return the absolute tolerance.
if self.rel is None:
if self.abs is not None:
return absolute_tolerance
# Figure out what the relative tolerance should be. ``self.rel`` is
# either None or a value specified by the user. This is done after
# we've made sure the user didn't ask for an absolute tolerance only,
# because we don't want to raise errors about the relative tolerance if
# we aren't even going to use it.
relative_tolerance = set_default(
self.rel, self.DEFAULT_RELATIVE_TOLERANCE
) * abs(self.expected)
if relative_tolerance < 0:
raise ValueError(
"relative tolerance can't be negative: {}".format(absolute_tolerance)
)
if math.isnan(relative_tolerance):
raise ValueError("relative tolerance can't be NaN.")
# Return the larger of the relative and absolute tolerances.
return max(relative_tolerance, absolute_tolerance)
class ApproxDecimal(ApproxScalar):
"""
Perform approximate comparisons where the expected value is a decimal.
"""
DEFAULT_ABSOLUTE_TOLERANCE = Decimal("1e-12")
DEFAULT_RELATIVE_TOLERANCE = Decimal("1e-6")
[docs]def approx(expected, rel=None, abs=None, nan_ok=False):
"""
Assert that two numbers (or two sets of numbers) are equal to each other
within some tolerance.
Due to the `intricacies of floating-point arithmetic`__, numbers that we
would intuitively expect to be equal are not always so::
>>> 0.1 + 0.2 == 0.3
False
__ https://docs.python.org/3/tutorial/floatingpoint.html
This problem is commonly encountered when writing tests, e.g. when making
sure that floating-point values are what you expect them to be. One way to
deal with this problem is to assert that two floating-point numbers are
equal to within some appropriate tolerance::
>>> abs((0.1 + 0.2) - 0.3) < 1e-6
True
However, comparisons like this are tedious to write and difficult to
understand. Furthermore, absolute comparisons like the one above are
usually discouraged because there's no tolerance that works well for all
situations. ``1e-6`` is good for numbers around ``1``, but too small for
very big numbers and too big for very small ones. It's better to express
the tolerance as a fraction of the expected value, but relative comparisons
like that are even more difficult to write correctly and concisely.
The ``approx`` class performs floating-point comparisons using a syntax
that's as intuitive as possible::
>>> from pytest import approx
>>> 0.1 + 0.2 == approx(0.3)
True
The same syntax also works for sequences of numbers::
>>> (0.1 + 0.2, 0.2 + 0.4) == approx((0.3, 0.6))
True
Dictionary *values*::
>>> {'a': 0.1 + 0.2, 'b': 0.2 + 0.4} == approx({'a': 0.3, 'b': 0.6})
True
``numpy`` arrays::
>>> import numpy as np # doctest: +SKIP
>>> np.array([0.1, 0.2]) + np.array([0.2, 0.4]) == approx(np.array([0.3, 0.6])) # doctest: +SKIP
True
And for a ``numpy`` array against a scalar::
>>> import numpy as np # doctest: +SKIP
>>> np.array([0.1, 0.2]) + np.array([0.2, 0.1]) == approx(0.3) # doctest: +SKIP
True
By default, ``approx`` considers numbers within a relative tolerance of
``1e-6`` (i.e. one part in a million) of its expected value to be equal.
This treatment would lead to surprising results if the expected value was
``0.0``, because nothing but ``0.0`` itself is relatively close to ``0.0``.
To handle this case less surprisingly, ``approx`` also considers numbers
within an absolute tolerance of ``1e-12`` of its expected value to be
equal. Infinity and NaN are special cases. Infinity is only considered
equal to itself, regardless of the relative tolerance. NaN is not
considered equal to anything by default, but you can make it be equal to
itself by setting the ``nan_ok`` argument to True. (This is meant to
facilitate comparing arrays that use NaN to mean "no data".)
Both the relative and absolute tolerances can be changed by passing
arguments to the ``approx`` constructor::
>>> 1.0001 == approx(1)
False
>>> 1.0001 == approx(1, rel=1e-3)
True
>>> 1.0001 == approx(1, abs=1e-3)
True
If you specify ``abs`` but not ``rel``, the comparison will not consider
the relative tolerance at all. In other words, two numbers that are within
the default relative tolerance of ``1e-6`` will still be considered unequal
if they exceed the specified absolute tolerance. If you specify both
``abs`` and ``rel``, the numbers will be considered equal if either
tolerance is met::
>>> 1 + 1e-8 == approx(1)
True
>>> 1 + 1e-8 == approx(1, abs=1e-12)
False
>>> 1 + 1e-8 == approx(1, rel=1e-6, abs=1e-12)
True
If you're thinking about using ``approx``, then you might want to know how
it compares to other good ways of comparing floating-point numbers. All of
these algorithms are based on relative and absolute tolerances and should
agree for the most part, but they do have meaningful differences:
- ``math.isclose(a, b, rel_tol=1e-9, abs_tol=0.0)``: True if the relative
tolerance is met w.r.t. either ``a`` or ``b`` or if the absolute
tolerance is met. Because the relative tolerance is calculated w.r.t.
both ``a`` and ``b``, this test is symmetric (i.e. neither ``a`` nor
``b`` is a "reference value"). You have to specify an absolute tolerance
if you want to compare to ``0.0`` because there is no tolerance by
default. Only available in python>=3.5. `More information...`__
__ https://docs.python.org/3/library/math.html#math.isclose
- ``numpy.isclose(a, b, rtol=1e-5, atol=1e-8)``: True if the difference
between ``a`` and ``b`` is less that the sum of the relative tolerance
w.r.t. ``b`` and the absolute tolerance. Because the relative tolerance
is only calculated w.r.t. ``b``, this test is asymmetric and you can
think of ``b`` as the reference value. Support for comparing sequences
is provided by ``numpy.allclose``. `More information...`__
__ http://docs.scipy.org/doc/numpy-1.10.0/reference/generated/numpy.isclose.html
- ``unittest.TestCase.assertAlmostEqual(a, b)``: True if ``a`` and ``b``
are within an absolute tolerance of ``1e-7``. No relative tolerance is
considered and the absolute tolerance cannot be changed, so this function
is not appropriate for very large or very small numbers. Also, it's only
available in subclasses of ``unittest.TestCase`` and it's ugly because it
doesn't follow PEP8. `More information...`__
__ https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertAlmostEqual
- ``a == pytest.approx(b, rel=1e-6, abs=1e-12)``: True if the relative
tolerance is met w.r.t. ``b`` or if the absolute tolerance is met.
Because the relative tolerance is only calculated w.r.t. ``b``, this test
is asymmetric and you can think of ``b`` as the reference value. In the
special case that you explicitly specify an absolute tolerance but not a
relative tolerance, only the absolute tolerance is considered.
.. warning::
.. versionchanged:: 3.2
In order to avoid inconsistent behavior, ``TypeError`` is
raised for ``>``, ``>=``, ``<`` and ``<=`` comparisons.
The example below illustrates the problem::
assert approx(0.1) > 0.1 + 1e-10 # calls approx(0.1).__gt__(0.1 + 1e-10)
assert 0.1 + 1e-10 > approx(0.1) # calls approx(0.1).__lt__(0.1 + 1e-10)
In the second example one expects ``approx(0.1).__le__(0.1 + 1e-10)``
to be called. But instead, ``approx(0.1).__lt__(0.1 + 1e-10)`` is used to
comparison. This is because the call hierarchy of rich comparisons
follows a fixed behavior. `More information...`__
__ https://docs.python.org/3/reference/datamodel.html#object.__ge__
"""
# Delegate the comparison to a class that knows how to deal with the type
# of the expected value (e.g. int, float, list, dict, numpy.array, etc).
#
# The primary responsibility of these classes is to implement ``__eq__()``
# and ``__repr__()``. The former is used to actually check if some
# "actual" value is equivalent to the given expected value within the
# allowed tolerance. The latter is used to show the user the expected
# value and tolerance, in the case that a test failed.
#
# The actual logic for making approximate comparisons can be found in
# ApproxScalar, which is used to compare individual numbers. All of the
# other Approx classes eventually delegate to this class. The ApproxBase
# class provides some convenient methods and overloads, but isn't really
# essential.
__tracebackhide__ = True
if isinstance(expected, Decimal):
cls = ApproxDecimal
elif isinstance(expected, Number):
cls = ApproxScalar
elif isinstance(expected, Mapping):
cls = ApproxMapping
elif _is_numpy_array(expected):
cls = ApproxNumpy
elif (
isinstance(expected, Iterable)
and isinstance(expected, Sized)
and not isinstance(expected, STRING_TYPES)
):
cls = ApproxSequencelike
else:
raise _non_numeric_type_error(expected, at=None)
return cls(expected, rel, abs, nan_ok)
def _is_numpy_array(obj):
"""
Return true if the given object is a numpy array. Make a special effort to
avoid importing numpy unless it's really necessary.
"""
import sys
np = sys.modules.get("numpy")
if np is not None:
return isinstance(obj, np.ndarray)
return False
# builtin pytest.raises helper
_E = TypeVar("_E", bound=BaseException)
@overload
def raises(
expected_exception: Union["Type[_E]", Tuple["Type[_E]", ...]],
*,
match: "Optional[Union[str, Pattern]]" = ...
) -> "RaisesContext[_E]":
... # pragma: no cover
@overload # noqa: F811
def raises(
expected_exception: Union["Type[_E]", Tuple["Type[_E]", ...]],
func: Callable,
*args: Any,
match: Optional[str] = ...,
**kwargs: Any
) -> Optional[_pytest._code.ExceptionInfo[_E]]:
... # pragma: no cover
[docs]def raises( # noqa: F811
expected_exception: Union["Type[_E]", Tuple["Type[_E]", ...]],
*args: Any,
match: Optional[Union[str, "Pattern"]] = None,
**kwargs: Any
) -> Union["RaisesContext[_E]", Optional[_pytest._code.ExceptionInfo[_E]]]:
r"""
Assert that a code block/function call raises ``expected_exception``
or raise a failure exception otherwise.
:kwparam match: if specified, a string containing a regular expression,
or a regular expression object, that is tested against the string
representation of the exception using ``re.search``. To match a literal
string that may contain `special characters`__, the pattern can
first be escaped with ``re.escape``.
__ https://docs.python.org/3/library/re.html#regular-expression-syntax
.. currentmodule:: _pytest._code
Use ``pytest.raises`` as a context manager, which will capture the exception of the given
type::
>>> with raises(ZeroDivisionError):
... 1/0
If the code block does not raise the expected exception (``ZeroDivisionError`` in the example
above), or no exception at all, the check will fail instead.
You can also use the keyword argument ``match`` to assert that the
exception matches a text or regex::
>>> with raises(ValueError, match='must be 0 or None'):
... raise ValueError("value must be 0 or None")
>>> with raises(ValueError, match=r'must be \d+$'):
... raise ValueError("value must be 42")
The context manager produces an :class:`ExceptionInfo` object which can be used to inspect the
details of the captured exception::
>>> with raises(ValueError) as exc_info:
... raise ValueError("value must be 42")
>>> assert exc_info.type is ValueError
>>> assert exc_info.value.args[0] == "value must be 42"
.. deprecated:: 4.1
In the context manager form you may use the keyword argument
``message`` to specify a custom failure message that will be displayed
in case the ``pytest.raises`` check fails. This has been deprecated as it
is considered error prone as users often mean to use ``match`` instead.
See :ref:`the deprecation docs <raises message deprecated>` for a workaround.
.. note::
When using ``pytest.raises`` as a context manager, it's worthwhile to
note that normal context manager rules apply and that the exception
raised *must* be the final line in the scope of the context manager.
Lines of code after that, within the scope of the context manager will
not be executed. For example::
>>> value = 15
>>> with raises(ValueError) as exc_info:
... if value > 10:
... raise ValueError("value must be <= 10")
... assert exc_info.type is ValueError # this will not execute
Instead, the following approach must be taken (note the difference in
scope)::
>>> with raises(ValueError) as exc_info:
... if value > 10:
... raise ValueError("value must be <= 10")
...
>>> assert exc_info.type is ValueError
**Using with** ``pytest.mark.parametrize``
When using :ref:`pytest.mark.parametrize ref`
it is possible to parametrize tests such that
some runs raise an exception and others do not.
See :ref:`parametrizing_conditional_raising` for an example.
**Legacy form**
It is possible to specify a callable by passing a to-be-called lambda::
>>> raises(ZeroDivisionError, lambda: 1/0)
<ExceptionInfo ...>
or you can specify an arbitrary callable with arguments::
>>> def f(x): return 1/x
...
>>> raises(ZeroDivisionError, f, 0)
<ExceptionInfo ...>
>>> raises(ZeroDivisionError, f, x=0)
<ExceptionInfo ...>
The form above is fully supported but discouraged for new code because the
context manager form is regarded as more readable and less error-prone.
.. note::
Similar to caught exception objects in Python, explicitly clearing
local references to returned ``ExceptionInfo`` objects can
help the Python interpreter speed up its garbage collection.
Clearing those references breaks a reference cycle
(``ExceptionInfo`` --> caught exception --> frame stack raising
the exception --> current frame stack --> local variables -->
``ExceptionInfo``) which makes Python keep all objects referenced
from that cycle (including all local variables in the current
frame) alive until the next cyclic garbage collection run. See the
official Python ``try`` statement documentation for more detailed
information.
"""
__tracebackhide__ = True
for exc in filterfalse(
inspect.isclass, always_iterable(expected_exception, BASE_TYPE)
):
msg = "exceptions must be derived from BaseException, not %s"
raise TypeError(msg % type(exc))
message = "DID NOT RAISE {}".format(expected_exception)
if not args:
if kwargs:
msg = "Unexpected keyword arguments passed to pytest.raises: "
msg += ", ".join(sorted(kwargs))
msg += "\nUse context-manager form instead?"
raise TypeError(msg)
return RaisesContext(expected_exception, message, match)
else:
func = args[0]
if not callable(func):
raise TypeError(
"{!r} object (type: {}) must be callable".format(func, type(func))
)
try:
func(*args[1:], **kwargs)
except expected_exception as e:
# We just caught the exception - there is a traceback.
assert e.__traceback__ is not None
return _pytest._code.ExceptionInfo.from_exc_info(
(type(e), e, e.__traceback__)
)
fail(message)
raises.Exception = fail.Exception # type: ignore
class RaisesContext(Generic[_E]):
def __init__(
self,
expected_exception: Union["Type[_E]", Tuple["Type[_E]", ...]],
message: str,
match_expr: Optional[Union[str, "Pattern"]] = None,
) -> None:
self.expected_exception = expected_exception
self.message = message
self.match_expr = match_expr
self.excinfo = None # type: Optional[_pytest._code.ExceptionInfo[_E]]
def __enter__(self) -> _pytest._code.ExceptionInfo[_E]:
self.excinfo = _pytest._code.ExceptionInfo.for_later()
return self.excinfo
def __exit__(
self,
exc_type: Optional["Type[BaseException]"],
exc_val: Optional[BaseException],
exc_tb: Optional[TracebackType],
) -> bool:
__tracebackhide__ = True
if exc_type is None:
fail(self.message)
assert self.excinfo is not None
if not issubclass(exc_type, self.expected_exception):
return False
# Cast to narrow the exception type now that it's verified.
exc_info = cast(
Tuple["Type[_E]", _E, TracebackType], (exc_type, exc_val, exc_tb)
)
self.excinfo.fill_unfilled(exc_info)
if self.match_expr is not None:
self.excinfo.match(self.match_expr)
return True
```