File: util.py

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"""Utilities for assertion debugging"""

import py
try:
    from collections import Sequence
except ImportError:
    Sequence = list

BuiltinAssertionError = py.builtin.builtins.AssertionError
u = py.builtin._totext

# The _reprcompare attribute on the util module is used by the new assertion
# interpretation code and assertion rewriter to detect this plugin was
# loaded and in turn call the hooks defined here as part of the
# DebugInterpreter.
_reprcompare = None


def format_explanation(explanation):
    """This formats an explanation

    Normally all embedded newlines are escaped, however there are
    three exceptions: \n{, \n} and \n~.  The first two are intended
    cover nested explanations, see function and attribute explanations
    for examples (.visit_Call(), visit_Attribute()).  The last one is
    for when one explanation needs to span multiple lines, e.g. when
    displaying diffs.
    """
    explanation = _collapse_false(explanation)
    lines = _split_explanation(explanation)
    result = _format_lines(lines)
    return u('\n').join(result)


def _collapse_false(explanation):
    """Collapse expansions of False

    So this strips out any "assert False\n{where False = ...\n}"
    blocks.
    """
    where = 0
    while True:
        start = where = explanation.find("False\n{False = ", where)
        if where == -1:
            break
        level = 0
        for i, c in enumerate(explanation[start:]):
            if c == "{":
                level += 1
            elif c == "}":
                level -= 1
                if not level:
                    break
        else:
            raise AssertionError("unbalanced braces: %r" % (explanation,))
        end = start + i
        where = end
        if explanation[end - 1] == '\n':
            explanation = (explanation[:start] + explanation[start+15:end-1] +
                           explanation[end+1:])
            where -= 17
    return explanation


def _split_explanation(explanation):
    """Return a list of individual lines in the explanation

    This will return a list of lines split on '\n{', '\n}' and '\n~'.
    Any other newlines will be escaped and appear in the line as the
    literal '\n' characters.
    """
    raw_lines = (explanation or u('')).split('\n')
    lines = [raw_lines[0]]
    for l in raw_lines[1:]:
        if l.startswith('{') or l.startswith('}') or l.startswith('~'):
            lines.append(l)
        else:
            lines[-1] += '\\n' + l
    return lines


def _format_lines(lines):
    """Format the individual lines

    This will replace the '{', '}' and '~' characters of our mini
    formatting language with the proper 'where ...', 'and ...' and ' +
    ...' text, taking care of indentation along the way.

    Return a list of formatted lines.
    """
    result = lines[:1]
    stack = [0]
    stackcnt = [0]
    for line in lines[1:]:
        if line.startswith('{'):
            if stackcnt[-1]:
                s = u('and   ')
            else:
                s = u('where ')
            stack.append(len(result))
            stackcnt[-1] += 1
            stackcnt.append(0)
            result.append(u(' +') + u('  ')*(len(stack)-1) + s + line[1:])
        elif line.startswith('}'):
            assert line.startswith('}')
            stack.pop()
            stackcnt.pop()
            result[stack[-1]] += line[1:]
        else:
            assert line.startswith('~')
            result.append(u('  ')*len(stack) + line[1:])
    assert len(stack) == 1
    return result


# Provide basestring in python3
try:
    basestring = basestring
except NameError:
    basestring = str


def assertrepr_compare(config, op, left, right):
    """Return specialised explanations for some operators/operands"""
    width = 80 - 15 - len(op) - 2  # 15 chars indentation, 1 space around op
    left_repr = py.io.saferepr(left, maxsize=int(width/2))
    right_repr = py.io.saferepr(right, maxsize=width-len(left_repr))
    summary = u('%s %s %s') % (left_repr, op, right_repr)

    issequence = lambda x: (isinstance(x, (list, tuple, Sequence))
                            and not isinstance(x, basestring))
    istext = lambda x: isinstance(x, basestring)
    isdict = lambda x: isinstance(x, dict)
    isset = lambda x: isinstance(x, (set, frozenset))

    verbose = config.getoption('verbose')
    explanation = None
    try:
        if op == '==':
            if istext(left) and istext(right):
                explanation = _diff_text(left, right, verbose)
            elif issequence(left) and issequence(right):
                explanation = _compare_eq_sequence(left, right, verbose)
            elif isset(left) and isset(right):
                explanation = _compare_eq_set(left, right, verbose)
            elif isdict(left) and isdict(right):
                explanation = _compare_eq_dict(left, right, verbose)
        elif op == 'not in':
            if istext(left) and istext(right):
                explanation = _notin_text(left, right, verbose)
    except Exception:
        excinfo = py.code.ExceptionInfo()
        explanation = [
            u('(pytest_assertion plugin: representation of details failed.  '
              'Probably an object has a faulty __repr__.)'),
            u(excinfo)]

    if not explanation:
        return None

    return [summary] + explanation


def _diff_text(left, right, verbose=False):
    """Return the explanation for the diff between text or bytes

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

    If the input are bytes they will be safely converted to text.
    """
    explanation = []
    if isinstance(left, py.builtin.bytes):
        left = u(repr(left)[1:-1]).replace(r'\n', '\n')
    if isinstance(right, py.builtin.bytes):
        right = u(repr(right)[1:-1]).replace(r'\n', '\n')
    if not verbose:
        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 = [u('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 += [u('Skipping %s identical trailing '
                                  'characters in diff, use -v to show') % i]
                left = left[:-i]
                right = right[:-i]
    explanation += [line.strip('\n')
                    for line in py.std.difflib.ndiff(left.splitlines(),
                                                     right.splitlines())]
    return explanation


def _compare_eq_sequence(left, right, verbose=False):
    explanation = []
    for i in range(min(len(left), len(right))):
        if left[i] != right[i]:
            explanation += [u('At index %s diff: %r != %r')
                            % (i, left[i], right[i])]
            break
    if len(left) > len(right):
        explanation += [u('Left contains more items, first extra item: %s')
                        % py.io.saferepr(left[len(right)],)]
    elif len(left) < len(right):
        explanation += [
            u('Right contains more items, first extra item: %s') %
            py.io.saferepr(right[len(left)],)]
    return explanation  # + _diff_text(py.std.pprint.pformat(left),
                        #             py.std.pprint.pformat(right))


def _compare_eq_set(left, right, verbose=False):
    explanation = []
    diff_left = left - right
    diff_right = right - left
    if diff_left:
        explanation.append(u('Extra items in the left set:'))
        for item in diff_left:
            explanation.append(py.io.saferepr(item))
    if diff_right:
        explanation.append(u('Extra items in the right set:'))
        for item in diff_right:
            explanation.append(py.io.saferepr(item))
    return explanation


def _compare_eq_dict(left, right, verbose=False):
    explanation = []
    common = set(left).intersection(set(right))
    same = dict((k, left[k]) for k in common if left[k] == right[k])
    if same and not verbose:
        explanation += [u('Omitting %s identical items, use -v to show') %
                        len(same)]
    elif same:
        explanation += [u('Common items:')]
        explanation += py.std.pprint.pformat(same).splitlines()
    diff = set(k for k in common if left[k] != right[k])
    if diff:
        explanation += [u('Differing items:')]
        for k in diff:
            explanation += [py.io.saferepr({k: left[k]}) + ' != ' +
                            py.io.saferepr({k: right[k]})]
    extra_left = set(left) - set(right)
    if extra_left:
        explanation.append(u('Left contains more items:'))
        explanation.extend(py.std.pprint.pformat(
            dict((k, left[k]) for k in extra_left)).splitlines())
    extra_right = set(right) - set(left)
    if extra_right:
        explanation.append(u('Right contains more items:'))
        explanation.extend(py.std.pprint.pformat(
            dict((k, right[k]) for k in extra_right)).splitlines())
    return explanation


def _notin_text(term, text, verbose=False):
    index = text.find(term)
    head = text[:index]
    tail = text[index+len(term):]
    correct_text = head + tail
    diff = _diff_text(correct_text, text, verbose)
    newdiff = [u('%s is contained here:') % py.io.saferepr(term, maxsize=42)]
    for line in diff:
        if line.startswith(u('Skipping')):
            continue
        if line.startswith(u('- ')):
            continue
        if line.startswith(u('+ ')):
            newdiff.append(u('  ') + line[2:])
        else:
            newdiff.append(line)
    return newdiff