Add effect.io, which has basic stdio intents/performers.

Author: radix

effect/io.py

@@ -0,0 +1,44 @@
+"""Intents and performers for basic user interaction.
+
+Use :obj:`effect.io.stdio_dispatcher` as a dispatcher for :obj:`Display` and
+:obj:`Prompt` that uses built-in Python standard io facilities.
+"""
+
+from __future__ import print_function
+import attr
+from six.moves import input
+
+from . import sync_performer, TypeDispatcher
+
+
+@attr.s
+class Display(object):
+    """Display some text to the user."""
+    output = attr.ib()
+
+
+@attr.s
+class Prompt(object):
+    """Get some input from the user, with a prompt."""
+    prompt = attr.ib()
+
+
+@sync_performer
+def perform_display_print(dispatcher, intent):
+    """Perform a :obj:`Display` intent by printing the output."""
+    print(intent.output)
+
+
+@sync_performer
+def perform_get_input_raw_input(dispatcher, intent):
+    """
+    Perform a :obj:`Prompt` intent by using ``raw_input`` (or ``input`` on
+    Python 3).
+    """
+    return input(intent.prompt)
+
+
+stdio_dispatcher = TypeDispatcher({
+    Display: perform_display_print,
+    Prompt: perform_get_input_raw_input,
+})

effect/test_io.py

@@ -0,0 +1,18 @@
+from . import Effect, sync_perform
+from .io import Display, Prompt, stdio_dispatcher
+
+
+def test_perform_display_print(capsys):
+    """The stdio dispatcher has a performer that prints output."""
+    assert sync_perform(stdio_dispatcher, Effect(Display("foo"))) is None
+    out, err = capsys.readouterr()
+    assert err == ''
+    assert out == 'foo\n'
+
+
+def test_perform_get_input_raw_input(monkeypatch):
+    """The stdio dispatcher has a performer that reads input."""
+    monkeypatch.setattr(
+        'effect.io.input',
+        lambda p: 'my name' if p == '> ' else 'boo')
+    assert sync_perform(stdio_dispatcher, Effect(Prompt('> '))) == 'my name'