Merge pull request #1026 from adqm/lazily_load_shells

Lazily load prompt_toolkit

xonsh/platform.py

@@ -93,13 +93,12 @@ def ptk_version_info():
         return None
 
 
-BEST_SHELL_TYPE = None
-""" The 'best' available shell type, either 'prompt_toollit' or 'readline'. """
-
-if ON_WINDOWS or has_prompt_toolkit():
-    BEST_SHELL_TYPE = 'prompt_toolkit'
-else:
-    BEST_SHELL_TYPE = 'readline'
+@lru_cache(1)
+def best_shell_type():
+    if ON_WINDOWS or has_prompt_toolkit():
+        return 'prompt_toolkit'
+    else:
+        return 'readline'
 
 
 @lru_cache(1)

xonsh/shell.py

@@ -7,7 +7,7 @@ from warnings import warn
 from xonsh import xontribs
 from xonsh.environ import xonshrc_context
 from xonsh.execer import Execer
-from xonsh.platform import (BEST_SHELL_TYPE, has_prompt_toolkit, ptk_version,
+from xonsh.platform import (best_shell_type, has_prompt_toolkit, ptk_version,
                             ptk_version_info)
 from xonsh.tools import XonshError
 
@@ -44,17 +44,16 @@ class Shell(object):
                            kwargs.get('cacheall', False))
         env = builtins.__xonsh_env__
         # pick a valid shell
-        if shell_type is not None:
-            env['SHELL_TYPE'] = shell_type
         shell_type = env.get('SHELL_TYPE')
         if shell_type == 'best' or shell_type is None:
-            shell_type = BEST_SHELL_TYPE
+            shell_type = best_shell_type()
         elif shell_type == 'random':
             shell_type = random.choice(('readline', 'prompt_toolkit'))
         if shell_type == 'prompt_toolkit':
             if not has_prompt_toolkit():
                 warn('prompt_toolkit is not available, using readline instead.')
-                shell_type = env['SHELL_TYPE'] = 'readline'
+                shell_type = 'readline'
+        env['SHELL_TYPE'] = shell_type
         # actually make the shell
         if shell_type == 'none':
             from xonsh.base_shell import BaseShell as shell_class

xonsh/tools.py

@@ -36,11 +36,6 @@ from collections import OrderedDict, Sequence, Set
 from xonsh.platform import (has_prompt_toolkit, scandir, win_unicode_console,
                             DEFAULT_ENCODING, ON_LINUX, ON_WINDOWS,
                             PYTHON_VERSION_INFO)
-if has_prompt_toolkit():
-    import prompt_toolkit
-else:
-    prompt_toolkit = None
-
 
 IS_SUPERUSER = ctypes.windll.shell32.IsUserAnAdmin() != 0 if ON_WINDOWS else os.getuid() == 0
 
@@ -861,6 +856,7 @@ def color_style():
 
 def _get_color_indexes(style_map):
     """ Generates the color and windows color index for a style """
+    import prompt_toolkit
     table = prompt_toolkit.terminal.win32_output.ColorLookupTable()
     pt_style = prompt_toolkit.styles.style_from_dict(style_map)
     for token in style_map:
@@ -882,7 +878,10 @@ def intensify_colors_for_cmd_exe(style_map, replace_colors=None):
        range used by the gray colors
     """
     modified_style = {}
-    if not ON_WINDOWS or prompt_toolkit is None:
+    stype = builtins.__xonsh_env__.get('SHELL_TYPE')
+    if (not ON_WINDOWS or
+            (stype not in ('prompt_toolkit', 'best')) or
+            (stype == 'best' and not has_prompt_toolkit())):
         return modified_style
     if replace_colors is None:
         replace_colors = {1: '#44ffff',  # subst blue with bright cyan
@@ -905,7 +904,10 @@ def expand_gray_colors_for_cmd_exe(style_map):
         in cmd.exe.
     """
     modified_style = {}
-    if not ON_WINDOWS or prompt_toolkit is None:
+    stype = builtins.__xonsh_env__.get('SHELL_TYPE')
+    if (not ON_WINDOWS or
+            (stype not in ('prompt_toolkit', 'best')) or
+            (stype == 'best' and not has_prompt_toolkit())):
         return modified_style
     for token, idx, rgb in _get_color_indexes(style_map):
         if idx == 7 and rgb: