py.test version: 3.6.0
Python version: 3.6.4

The result attribute of CallInfo objects is assigned in __init__ as the result of calling the test function. This means that result is only defined after the test function has finished executing.
If however, the test function extracts local variables from the stack (and does anything causing __repr__ to be called on them) this causes an AttributeError since CallInfo.__repr__ expects result to be defined.

Minimum example:

import sys
from traceback import print_list, StackSummary, walk_stack


def print_stack():
    stack = StackSummary.extract(walk_stack(sys._getframe().f_back), capture_locals=True)
    stack.reverse()
    print_list(stack)


def test_bla():
    print_stack()
    # ^ This will crash with `AttributeError: 'CallInfo' object has no attribute 'result'`
    assert 1 == 1