Context managers confuse branch coverage

[nedbat]

In this code:

from contextlib import contextmanager

@contextmanager
def dummy():
    yield

for i in range(10):
    with dummy():
        print "hello"  # line 9
    print "bye"
print "done"   # line 11

Line 9 claims to have an untaken branch to line 11.

---

• Bitbucket: https://bitbucket.org/ned/coveragepy/issue/146

[nedbat]

Original comment by Wichert Akkerman (Bitbucket: wichert, GitHub: wichert)

---

FWIW: I just ran into this as well using Python 2.7.3 and mock 1.0b1.

[nedbat]

Original comment by Laurens Van Houtven (Bitbucket: lvh, GitHub: lvh)

---

I ran in to this today as well, by opening files using the with statement inside a for loop.

[nedbat]

Another report of this from lvh:

class T(unittest.TestCase):
    def setUp(self):
        # SNIP SNIP
        for fileName in ["index.html", "style.css", "app.js"]:
            with location.child(fileName).open("w") as f:
                f.write("base {ext}".format(ext=fileName.split(".")[-1])) # NO JUMP TO NEXT LINE

        f = frontend.FrontEnd(store=s, build=b, domain="frontend.test")

[nedbat]

Issue #248 was marked as a duplicate of this issue.

[nedbat]

Original comment by stefano_palazzo (Bitbucket: stefano_palazzo, GitHub: Unknown)

---

Here's an example that probably describes the same issue:

#!python

class Context:

    def __init__(self, do_raise):
        self.do_raise = do_raise

    def __enter__(self):
        if self.do_raise:
            raise FileNotFoundError()
        return self

    def __exit__(self, *exc_info):
        pass


def load(do_raise):
    try:
        with Context(do_raise) as f:
            print(f)
    except FileNotFoundError:
        pass


load(True)
load(False)

With "print(f)" claiming to have an untaken branch to "except FileNotFoundError:".

[nedbat]

Original comment by Anthony Sottile (Bitbucket: asottile, GitHub: asottile)

---

Interestingly the following example seems to only plague 2.6 (not 2.7, 3.3, 3.4, pypy from my testing)

from __future__ import print_function
from __future__ import unicode_literals

import contextlib


@contextlib.contextmanager
def noop():
    yield


def test_foo():
    with noop():
        with noop():
            print('1')
        print('2')

[nedbat]

Issue #319 was marked as a duplicate of this issue.

[nedbat]

Issue #362 was marked as a duplicate of this issue.

[nedbat]

Original comment by Jessamyn Smith (Bitbucket: jessamynsmith, GitHub: jessamynsmith)

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As Ned just taught me, if this is plaguing you, you can add the following to the erroneously not-covered line:

pragma: no branch

[nedbat]

Original comment by Buck Evan (Bitbucket: bukzor, GitHub: bukzor)

---

@asottile I've just run into this issue on python 2.7.6.

#!python

class Trivial:
    def __enter__(self):
        print('enter!')
    def __exit__(self, type, value, tb):
        print('exit!')

def demo():
    try:
        with Trivial():
            print('ok')  # this line flagged as missed branch
    except:
        pass

[nedbat]

Original comment by Dan Jones (Bitbucket: dannosaur, GitHub: dannosaur)

---

Ran into this as well on Python 2.7.10 (coverage 3.7.1);

#!python

class Something:
    def something_else(self):
        try:
            with transaction.atomic():
                # ...
                print "x"
            print "y"
        except Exception:
           print "z"

"print x" has a missed branch to "except Exception:".

[nedbat]

This will be fixed when the ast-branch is merged.

[nedbat]

Issue #384 was marked as a duplicate of this issue.

[nedbat]

This is fixed in 44719bd (bb), which will be 4.1

[nedbat]

Issue #470 was marked as a duplicate of this issue.

[nedbat]

Issue #473 was marked as a duplicate of this issue.