pytest掃盲14--pytest.raises()函數文檔及在參數化中處理異常

pytest.raises() 函數文檔如下：

def raises(  # noqa: F811
    expected_exception: Union["Type[_E]", Tuple["Type[_E]", ...]],
    *args: Any,
    **kwargs: Any
) -> Union["RaisesContext[_E]", _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``.

        (This is only used when ``pytest.raises`` is used as a context manager,
        and passed through to the function otherwise.
        When using ``pytest.raises`` as a function, you can use:
        ``pytest.raises(Exc, func, match="passed on").match("my pattern")``.)　　

        __ https://docs.python.org/3/library/re.html#regular-expression-syntax　　# 正則表達式官方文檔

    .. currentmodule:: _pytest._code

    Use ``pytest.raises`` as a context manager, which will capture the exception of the given
    type::　　# 使用 pytest.raises 作為上下文管理器，捕獲給定異常類型.

        >>> 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.　　# 代碼中未發生異常，會檢查失敗

    You can also use the keyword argument ``match`` to assert that the
    exception matches a text or regex::　　# 使用關鍵字或正則表達式匹配異常文本

        >>> 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::　　　　# 上下文管理器會產生一個對象 ExceptionInfo，用於檢查異常的詳細信息　　
　　
        >>> with raises(ValueError) as exc_info:
        ...     raise ValueError("value must be 42")
        >>> assert exc_info.type is ValueError　　# 異常類型，異常類型只能是標准類型　　.type
        >>> assert exc_info.value.args[0] == "value must be 42"　　# 異常值，元祖　　.value.arg[index]

    .. 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::　　# 這里是關於 pytest.raises 作用范圍的例子，只能在with范圍內引發異常，之后的代碼不會只想。要使用必須跳出 with 作用范圍

           >>> 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``　　# 使用 pytest.mark.parametrize 進行參數化，使某些運行引發異常，其他運行正常執行

    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**　　# 這里是直接使用 raises() 調用參數的一種用法（不推薦）

    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.　　# 關於碎片整理的信息

    .. 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.
        More detailed information can be found in the official Python
        documentation for :ref:`the try statement <python:try>`.
    """

 

利用raise()函數文檔給出的例子再優化下 parametrize 參數化的例子（注意標紅的部分，在參數化數據中直接處理異常）：

更多關於 parametrize 的用法見官方文檔：　　https://docs.pytest.org/en/latest/example/parametrize.html

# File  : test_demo_14.py
# IDE   : PyCharm

import pytest

def division(a, b):
    return int(a / b)

@pytest.mark.parametrize('a, b, c', [(4, 2, 2), (0, 2, 0), (1, 0, pytest.raises(ZeroDivisionError)), (6, 8, 0)], ids=['整除', '被除數為0', '除數為0', '非整除'])
def test_2(a, b, c):
    '''使用 pytest.raises 接收異常'''
    if b == 0:
        with c:
            assert division(a, b) is not None
    else:
        assert division(a, b) == c

執行后：

 

此例子旨在說明，在進行參數化時，對於預期會失敗的用例，在構造測試數據時，也可以采用 python.raise() 對異常進行捕獲，甚至斷言。