AttributeError: 'ExceptionInfo' object has no attribute 'traceback' when using pytest to assert exceptions

Question

I need to assert an error message using py.test,

import pandas as pd
import numpy as np

from inv_exception_store import InvAmtValError

MAX_INV_VAL = 10000000.0
MIN_INV_VAL = 0.0


class Invoices:

    def __init__(self, data=None):
        if data is None:
            self.__invoices = pd.Series([], dtype=np.float32)
        else:
            self.__invoices = pd.Series(pd.Series(data).astype(np.float32))

    def addInvoice(self, amount):
        try:
            if self.__invoices.size > MAX_INV_SIZE:
                raise InvNumError
            elif amount > MAX_INV_VAL or amount < MIN_INV_VAL:
                raise InvAmtValError(amount)
            else:
                self.__invoices = self.__invoices.append(pd.Series(amount).astype(np.float32), ignore_index=True)
        except (InvNumError, InvAmtValError) as e:
            print(str(e))


class InvAmtValError(Exception):
    def __init__(self, amount, message=None):
        if message is None:
            if amount > 100000000.0:
                message = 'The invoice amount(s) {} is invalid since it is > $100,000,00.00'.format(amount)
            elif amount < 0.0:
                message = 'The invoice amount(s) {} is invalid since it is < $0.00'.format(amount)
            else:
                message = 'The invoice amount(s) {} is invalid'.format(amount)

        super(InvAmtValError, self).__init__(str(self.__class__.__name__) + ': ' + message)
        self.message = message

    def __str__(self):
        return self.message

class TestInvoice(object):
        def test_invalid_inv_amount_err(self):
            with pytest.raises(InvAmtValError) as e:
                invoices = Invoices()

                invoices.addInvoice(-1.2)

                assert str(e) == 'The invoice amount(s) -1.2 is invalid since it is < $0.00'

                invoices.addInvoice(100000000.1)

                assert str(e) == 'The invoice amount(s) 100000000.1 is invalid since it is > $100,000,00.00'

by running the test, I got,

self = <ExceptionInfo AttributeError tblen=2>

    def __str__(self):
>       entry = self.traceback[-1]
E       AttributeError: 'ExceptionInfo' object has no attribute 'traceback'

I am wondering how to make py.test work for asserting exception here.

UPDATE. Tried the solution suggested,

    def test_invalid_min_inv_amount_err(self):
        with pytest.raises(InvAmtValError) as e:
            invoices = Invoices()

            invoices.addInvoice(-1.2)
        assert str(e) == 'The invoice amount(s) -1.2 is invalid since it is < $0.00'
        assert e.type == InvAmtValError

got

>           invoices.addInvoice(-1.2)
E           Failed: DID NOT RAISE

Answer 1

You can't use the ExceptionInfo inside the with pytest.raises context. Run the code that is expected to raise in the context, work with the exception info outside:

with pytest.raises(InvAmtValError) as e:
    invoices = InvoiceStats()
    invoices.addInvoice(-1.2)

assert str(e) == 'The invoice amount(s) -1.2 is invalid since it is < $0.00'
assert e.type == InvAmtValError  # etc

However, if you just want to assert the exception message, the idiomatic way would be passing the expected message directly to pytest.raises:

expected = 'The invoice amount(s) -1.2 is invalid since it is < $0.00'
with pytest.raises(InvAmtValError, match=expected):
    invoices = InvoiceStats()
    invoices.addInvoice(-1.2)

expected = 'The invoice amount(s) 100000000.1 is invalid since it is > $100,000,00.00'
with pytest.raises(InvAmtValError, match=expected):
    invoices = InvoiceStats()
    invoices.addInvoice(100000000.1)

UPDATE. Tried the solution suggested, got:

>           invoices.addInvoice(-1.2)
E           Failed: DID NOT RAISE

That's because the exception is indeed not raised in the addInvoice method - it is raised inside the try block and immediately catched afterwards. Either remove the try block altogether, or reraise the exception:

try:
    raise InvAmtValError(amount)
except InvAmtValError as e:
    print(str(e))
    raise e