1 files changed, 49 insertions, 0 deletions
diff --git a/alembic/util/os_helpers.py b/alembic/util/os_helpers.py
new file mode 100644
index 0000000..ccbfa11
--- /dev/null
+++ b/alembic/util/os_helpers.py
@@ -0,0 +1,49 @@
+from os.path import join, exists
+from subprocess import check_call
+import os
+
+
+def open_in_editor(filename, environ=None):
+    '''
+    Opens the given file in a text editor. If the environment vaiable ``EDITOR``
+    is set, this is taken as preference.
+
+    Otherwise, a list of commonly installed editors is tried.
+
+    If no editor matches, an :py:exc:`OSError` is raised.
+
+    :param filename: The filename to open. Will be passed  verbatim to the
+        editor command.
+    :param environ: An optional drop-in replacement for ``os.environ``. Used
+        mainly for testing.
+    '''
+
+    environ = environ or os.environ
+
+    # Look for an editor. Prefer the user's choice by env-var, fall back to most
+    # commonly installed editor (nano/vim)
+    candidates = [
+        '/usr/bin/sensible-editor',
+        '/usr/bin/nano',
+        '/usr/bin/vim',
+    ]
+
+    if 'EDITOR' in environ:
+        user_choice = environ['EDITOR']
+        if '/' not in user_choice:
+            # Assuming this is on the PATH, we need to determine it's absolute
+            # location. Otherwise, ``check_call`` will fail
+            for path in environ.get('PATH', '').split(os.pathsep):
+                if exists(join(path, user_choice)):
+                    user_choice = join(path, user_choice)
+                    break
+        candidates.insert(0, user_choice)
+
+    for path in candidates:
+        if exists(path):
+            editor = path
+            break
+    else:
+        raise OSError('No suitable editor found. Please set the '
+                      '"EDITOR" environment variable')
+    check_call([editor, filename])