A few issues from our Python analyzer:

* Dangerous mutable default argument passed in functions

``` def some_func(arg=[1,2,3]):

    ...

```

which should be

``` def some_func(arg=None):

    if arg is None: arg = [1,2,3]
    ...

```

* `yield` used inside a comprehension (which breaks code in Python 3.8)

* file opened with the "r" flag, but a write is attempted on the file

* i/o detected on a closed file descriptor

* providing an unexpected keyword argument in a function call