Allow querying non-host python intepreters

This way you can install once (for example via pipx) and reuse it for any
existing python environment.

Signed-off-by: Bernat Gabor <bgabor8@bloomberg.net>

.travis.yml

@@ -15,7 +15,7 @@ addons:
       - graphviz
 before_install:
   - pip install -U pip>=8.0.2
-  - pip install pytest
+  - pip install pytest virtualenv>=20
   - pip install graphviz
 install: pip install .
 script: pytest -v tests/test_pipdeptree.py

dev-requirements.txt

@@ -3,3 +3,4 @@ pytest-cov
 jinja2
 ipython
 flake8
+virtualenv>=20

pipdeptree.py

@@ -7,6 +7,7 @@
 from operator import attrgetter
 import json
 from importlib import import_module
+import subprocess
 
 try:
     from collections import OrderedDict
@@ -18,6 +19,17 @@
 except ImportError:
     from collections import Mapping
 
+
+def _patch_sub_invocation():
+    if os.environ.get('_PIP_DEPTREE_SUB_CALL') == '1':
+        here = os.path.abspath(os.path.dirname(__file__))
+        if os.path.abspath(sys.path[0]) == here:
+            del sys.path[0]
+
+
+# needs to happen before we import pip as the workset is calculated at load
+_patch_sub_invocation()
+
 try:
     from pip._internal.utils.misc import get_installed_distributions
     from pip._internal.operations.freeze import FrozenRequirement
@@ -711,6 +723,9 @@ def get_parser():
                         version='{0}'.format(__version__))
     parser.add_argument('-f', '--freeze', action='store_true',
                         help='Print names so as to write freeze files')
+    parser.add_argument('--python', default=sys.executable,
+                        help='Python to use to look for packages in it (default: where'
+                             ' installed)')
     parser.add_argument('-a', '--all', action='store_true',
                         help='list all deps at top level')
     parser.add_argument('-l', '--local-only',
@@ -777,7 +792,22 @@ def _get_args():
 
 def main():
     args = _get_args()
-
+    of_python = os.path.abspath(args.python)
+    if of_python != os.path.abspath(sys.executable):
+        if args.output_format:
+            print("graphviz functionality is not supported when querying"
+                  " non-host python", file=sys.stderr)
+            raise SystemExit(1)
+        argv = sys.argv[1:]
+        py_at = argv.index('--python')
+        del argv[py_at]
+        del argv[py_at]
+        cmd = [args.python, __file__]
+        cmd.extend(argv)
+        env = os.environ.copy()
+        env['_PIP_DEPTREE_SUB_CALL'] = '1'
+        return_code = subprocess.call(cmd, env=env)
+        return return_code
     pkgs = get_installed_distributions(local_only=args.local_only,
                                        user_only=args.user_only)
 

tests/test_pipdeptree.py

@@ -7,6 +7,7 @@
     import mock
 
 import pytest
+import virtualenv
 
 import pipdeptree as p
 
@@ -520,3 +521,25 @@ def test_parser_svg():
     args = parser.parse_args(['--graph-output', 'svg'])
     assert args.output_format == 'svg'
     assert not args.json
+
+
+def test_custom_interpreter(tmp_path, monkeypatch, capfd):
+    result = virtualenv.cli_run([str(tmp_path), '--activators', ''])
+    cmd = [sys.executable, '--python', str(result.creator.exe)]
+    monkeypatch.setattr(sys, 'argv', cmd)
+    p.main()
+    out, _ = capfd.readouterr()
+    found = {i.split('==')[0] for i in out.splitlines()}
+    assert found == {'pip', 'setuptools', 'wheel'}, out
+
+    monkeypatch.setattr(sys, 'argv', cmd + ['--graph-output', 'something'])
+    with pytest.raises(SystemExit) as context:
+        p.main()
+    out, err = capfd.readouterr()
+    assert context.value.code == 1
+    assert not out
+    assert err == 'graphviz functionality is not supported when querying' \
+                  ' non-host python\n'
+
+
+

tox.ini

@@ -15,3 +15,4 @@ deps =
     pip>=8.0.2
     pytest
     pytest-cov
+    virtualenv>=20