# Buggy code
def find_a_system_python(line):
    """Find a Python installation from a given line.

    This tries to parse the line in various of ways:

    * Looks like an absolute path? Use it directly.
    * Looks like a py.exe call? Use py.exe to get the executable.
    * Starts with "py" something? Looks like a python command. Try to find it
      in PATH, and use it directly.
    * Search for "python" and "pythonX.Y" executables in PATH to find a match.
    * Nothing fits, return None.
    """
    if not line:
        return None
    if os.path.isabs(line):
        return line
    from .vendor.pythonfinder import Finder

    finder = Finder(system=False, global_search=True)
    if (line.startswith("py ") or line.startswith("py.exe ")) and os.name == "nt":
        line = line.split(" ", 1)[1].lstrip("-")
    elif line.startswith("py"):
        python_entry = finder.which(line)
        if python_entry:
            return python_entry.path.as_posix()
        return None
    python_entry = finder.find_python_version(line)
    if not python_entry:
        python_entry = finder.which("python{0}".format(line))
    if python_entry:
        return python_entry.path.as_posix()
    return None


# Traceback (json.decoder.JSONDecodeError)
$ pipenv check --system
Checking PEP 508 requirements...
Traceback (most recent call last):
File "/usr/local/bin/pipenv", line 11, in <module>
sys.exit(cli())
File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/core.py", line 722, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/core.py", line 697, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/core.py", line 1066, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/core.py", line 895, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python3.5/dist-packages/pipenv/vendor/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/pipenv/cli.py", line 762, in check
pypi_mirror=pypi_mirror
File "/usr/local/lib/python3.5/dist-packages/pipenv/core.py", line 2295, in do_check
results = simplejson.loads(c.out)
File "/usr/lib/python3.5/json/__init__.py", line 319, in loads
return _default_decoder.decode(s)
File "/usr/lib/python3.5/json/decoder.py", line 339, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
File "/usr/lib/python3.5/json/decoder.py", line 357, in raw_decode
raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

# Fixed code
def find_a_system_python(line):
    """Find a Python installation from a given line.

    This tries to parse the line in various of ways:

    * Looks like an absolute path? Use it directly.
    * Looks like a py.exe call? Use py.exe to get the executable.
    * Starts with "py" something? Looks like a python command. Try to find it
      in PATH, and use it directly.
    * Search for "python" and "pythonX.Y" executables in PATH to find a match.
    * Nothing fits, return None.
    """

    if os.path.isabs(line):
        return line
    from .vendor.pythonfinder import Finder

    finder = Finder(system=False, global_search=True)
    if not line:
        return next(iter(finder.find_all_python_versions()), None)
    # Use the windows finder executable
    if (line.startswith("py ") or line.startswith("py.exe ")) and os.name == "nt":
        line = line.split(" ", 1)[1].lstrip("-")
    python_entry = find_python(finder, line)
    return python_entry