Support REPL command history.

pex/pex.py

@@ -671,6 +671,21 @@ def execute_interpreter(self):
                 sys.argv = args
                 return self.execute_content(arg, content)
         else:
+            if self._vars.PEX_INTERPRETER_HISTORY:
+                import atexit
+                import readline
+
+                histfile = os.path.expanduser(self._vars.PEX_INTERPRETER_HISTORY_FILE)
+                try:
+                    readline.read_history_file(histfile)
+                    readline.set_history_length(1000)
+                except OSError as e:
+                    sys.stderr.write(
+                        "Failed to read history file at {} due to: {}".format(histfile, e)
+                    )
+
+                atexit.register(readline.write_history_file, histfile)
+
             self.demote_bootstrap()
 
             import code

pex/variables.py

@@ -189,8 +189,8 @@ def from_rc(cls, rc=None):
         """
         ret_vars = {}  # type: Dict[str, str]
         rc_locations = [
-            "/etc/pexrc",
-            "~/.pexrc",
+            os.path.join(os.sep, "etc", "pexrc"),
+            os.path.join("~", ".pexrc"),
             os.path.join(os.path.dirname(sys.argv[0]), ".pexrc"),
         ]
         if rc:
@@ -520,6 +520,32 @@ def PEX_INTERPRETER(self):
         """
         return self._get_bool("PEX_INTERPRETER")
 
+    @defaulted_property(default=False)
+    def PEX_INTERPRETER_HISTORY(self):
+        # type: () -> bool
+        """Boolean.
+
+        IF PEX_INTERPRETER is true, use a command history file for REPL user convenience.
+        The location of the history file is determined by PEX_INTERPRETER_HISTORY_FILE.
+
+        Note: Only supported on CPython interpreters.
+
+        Default: false.
+        """
+        return self._get_bool("PEX_INTERPRETER_HISTORY")
+
+    @defaulted_property(default=os.path.join("~", ".python_history"))
+    def PEX_INTERPRETER_HISTORY_FILE(self):
+        # type: () -> str
+        """File.
+
+        IF PEX_INTERPRETER_HISTORY is true, use this history file.
+        The default is the standard CPython interpreter history location.
+
+        Default: ~/.python_history.
+        """
+        return self._get_string("PEX_INTERPRETER_HISTORY_FILE")
+
     @property
     def PEX_MODULE(self):
         # type: () -> Optional[str]
@@ -607,7 +633,7 @@ def PEX_EXTRA_SYS_PATH(self):
         )
         return self._maybe_get_path_tuple("PEX_EXTRA_SYS_PATH") or ()
 
-    @defaulted_property(default="~/.pex")
+    @defaulted_property(default=os.path.join("~", ".pex"))
     def PEX_ROOT(self):
         # type: () -> str
         """Directory.

pex/venv/pex.py

@@ -401,6 +401,8 @@ def sys_executable_paths():
                     "PEX_EXTRA_SYS_PATH",
                     "PEX_VENV_BIN_PATH",
                     "PEX_INTERPRETER",
+                    "PEX_INTERPRETER_HISTORY",
+                    "PEX_INTERPRETER_HISTORY_FILE",
                     "PEX_SCRIPT",
                     "PEX_MODULE",
                     # This is used when loading ENV (Variables()):
@@ -474,6 +476,13 @@ def sys_executable_paths():
                 sys.exit(1)
             is_exec_override = len(pex_overrides) == 1
 
+            pex_interpreter_history = os.environ.get(
+                "PEX_INTERPRETER_HISTORY", "false"
+            ).lower() in ("1", "true")
+            pex_interpreter_history_file = os.environ.get(
+                "PEX_INTERPRETER_HISTORY_FILE", os.path.join("~", ".python_history")
+            )
+
             if {strip_pex_env!r}:
                 for key in list(os.environ):
                     if key.startswith("PEX_"):
@@ -504,6 +513,19 @@ def sys_executable_paths():
                 # See https://docs.python.org/3/library/sys.html#sys.path
                 sys.path.insert(0, "")
 
+                if pex_interpreter_history:
+                    import atexit
+                    import readline
+
+                    histfile = os.path.expanduser(pex_interpreter_history_file)
+                    try:
+                        readline.read_history_file(histfile)
+                        readline.set_history_length(1000)
+                    except OSError:
+                        pass
+
+                    atexit.register(readline.write_history_file, histfile)
+
             if entry_point == PEX_INTERPRETER_ENTRYPOINT and len(sys.argv) > 1:
                 args = sys.argv[1:]
 

tests/integration/test_integration.py

@@ -28,6 +28,7 @@
 from pex.requirements import LogicalLine, PyPIRequirement, parse_requirement_file
 from pex.testing import (
     IS_MAC,
+    IS_PYPY,
     NOT_CPYTHON27,
     NOT_CPYTHON27_OR_OSX,
     PY38,
@@ -227,6 +228,39 @@ def test_pex_repl_built():
         assert b">>>" in stdout
 
 
+@pytest.mark.skipif(
+    IS_PYPY or IS_MAC,
+    reason="REPL history is only supported on CPython. It works on macOS in an interactive "
+    "terminal, but this test fails in CI on macOS with `Inappropriate ioctl for device`, "
+    "because readline.read_history_file expects a tty on stdout. The linux tests will have "
+    "to suffice for now.",
+)
+@pytest.mark.parametrize("venv_pex", [False, True])
+def test_pex_repl_history(venv_pex):
+    # type: (...) -> None
+    """Tests enabling REPL command history."""
+    stdin_payload = b"import sys; import readline; print(readline.get_history_item(1)); sys.exit(3)"
+
+    with temporary_dir() as output_dir:
+        # Create a dummy temporary pex with no entrypoint.
+        pex_path = os.path.join(output_dir, "dummy.pex")
+        results = run_pex_command(
+            ["--disable-cache", "-o", pex_path] + (["--venv"] if venv_pex else [])
+        )
+        results.assert_success()
+
+        history_file = os.path.join(output_dir, ".python_history")
+        with open(history_file, "w") as fp:
+            fp.write("2 + 2\n")
+
+        # Test that the REPL can see the history.
+        env = {"PEX_INTERPRETER_HISTORY": "1", "PEX_INTERPRETER_HISTORY_FILE": history_file}
+        stdout, rc = run_simple_pex(pex_path, stdin=stdin_payload, env=env)
+        assert rc == 3, "Failed with: {}".format(stdout.decode("utf-8"))
+        assert b">>>" in stdout
+        assert b"2 + 2" in stdout
+
+
 @pytest.mark.skipif(WINDOWS, reason="No symlinks on windows")
 def test_pex_python_symlink():
     # type: () -> None