Function _diff_text

src/_pytest/assertion/util.py:215–260

Return the explanation for the diff between text. Unless --verbose is used this will skip leading and trailing characters which are identical to keep the diff minimal.

(left: str, right: str, verbose: int = 0)

def _diff_text(left: str, right: str, verbose: int = 0) -> List[str]:
    """Return the explanation for the diff between text.

    Unless --verbose is used this will skip leading and trailing
    characters which are identical to keep the diff minimal.
    """
    from difflib import ndiff

    explanation: List[str] = []

    if verbose < 1:
        i = 0  # just in case left or right has zero length
        for i in range(min(len(left), len(right))):
            if left[i] != right[i]:
                break
        if i > 42:
            i -= 10  # Provide some context
            explanation = [
                "Skipping %s identical leading characters in diff, use -v to show" % i
            ]
            left = left[i:]
            right = right[i:]
        if len(left) == len(right):
            for i in range(len(left)):
                if left[-i] != right[-i]:
                    break
            if i > 42:
                i -= 10  # Provide some context
                explanation += [
                    "Skipping {} identical trailing "
                    "characters in diff, use -v to show".format(i)
                ]
                left = left[:-i]
                right = right[:-i]
    keepends = True
    if left.isspace() or right.isspace():
        left = repr(str(left))
        right = repr(str(right))
        explanation += ["Strings contain only whitespace, escaping them using repr()"]
    # "right" is the expected base against which we compare "left",
    # see https://github.com/pytest-dev/pytest/issues/3333
    explanation += [
        line.strip("\n")
        for line in ndiff(right.splitlines(keepends), left.splitlines(keepends))
    ]
    return explanation


def _compare_eq_verbose(left: Any, right: Any) -> List[str]: