Allows overriding PIP_EXISTS_ACTION environment variable (it was fo…

…rced to `w`) (#3738)

Allows overriding `PIP_EXISTS_ACTION` environment variable (it was forced to `w`)

news/3738.feature.rst

@@ -0,0 +1,3 @@
+Allow overriding PIP_EXISTS_ACTION evironment variable (value is passed to pip install). 
+Possible values here: https://pip.pypa.io/en/stable/reference/pip/#exists-action-option
+Useful when you need to `PIP_EXISTS_ACTION=i` (ignore existing packages) - great for CI environments, where you need really fast setup.

pipenv/core.py

@@ -26,7 +26,7 @@
     PIPENV_CACHE_DIR, PIPENV_COLORBLIND, PIPENV_DEFAULT_PYTHON_VERSION,
     PIPENV_DONT_USE_PYENV, PIPENV_HIDE_EMOJIS, PIPENV_MAX_SUBPROCESS,
     PIPENV_PYUP_API_KEY, PIPENV_SHELL_FANCY, PIPENV_SKIP_VALIDATION,
-    PIPENV_YES, SESSION_IS_INTERACTIVE
+    PIPENV_YES, SESSION_IS_INTERACTIVE, PIP_EXISTS_ACTION
 )
 from .project import Project, SourceNotFound
 from .utils import (
@@ -1513,7 +1513,7 @@ def pip_install(
         "PIP_DESTINATION_DIR": vistir.misc.fs_str(
             cache_dir.joinpath("pkgs").as_posix()
         ),
-        "PIP_EXISTS_ACTION": vistir.misc.fs_str("w"),
+        "PIP_EXISTS_ACTION": vistir.misc.fs_str(PIP_EXISTS_ACTION or "w"),
         "PATH": vistir.misc.fs_str(os.environ.get("PATH")),
     }
     if src:

pipenv/environments.py

@@ -234,6 +234,12 @@ def _is_env_truthy(name):
 NOTE: This only affects the ``install`` and ``uninstall`` commands.
 """
 
+PIP_EXISTS_ACTION = os.environ.get("PIP_EXISTS_ACTION", "w")
+"""Specifies the value for pip's --exists-action option
+
+Defaullts to (w)ipe
+"""
+
 PIPENV_RESOLVE_VCS = _is_env_truthy(os.environ.get("PIPENV_RESOLVE_VCS", 'true'))
 """Tells Pipenv whether to resolve all VCS dependencies in full.
 
@@ -242,7 +248,6 @@ def _is_env_truthy(name):
 approach, you may set this to '0', 'off', or 'false'.
 """
 
-
 PIPENV_PYUP_API_KEY = os.environ.get(
     "PIPENV_PYUP_API_KEY", "1ab8d58f-5122e025-83674263-bc1e79e0"
 )