Introduce --color option to force colored output

With introducing blessings module (from 0.4) which automatically
determines color for output, depending on whether stdout has tty
or not (i.e. piped), we should have a way to 'force' colored output.

For example, `watch --color gpustat` was always suppressing color.
Using the `--color` or `--force-color` option, we can always have
the colored output even if stdout is not a tty.

README.md

@@ -16,15 +16,16 @@ Usage
 
 Options:
 
-* `--no-color`        : Suppress color (by default, color is enabled)
+* `--color`           : Force colored output (even when stdout is not a tty)
+* `--no-color`        : Suppress color (by default, color is automatically enabled)
 * `-u`, `--show-user` : Display username of the process owner
 * `-c`, `--show-cmd`  : Display the process name
 * `-p`, `--show-pid`  : Display PID of the process
 * `--json`            : JSON Output (Experimental, [#10][gh-issue-10])
 
 ### Tips
 
-- To periodically watch, try `watch --color -n1.0 gpustat` (built-in watch support will be added soon).
+- To periodically watch, try `watch --color -n1.0 gpustat --color` (built-in watch support will be added soon).
 - Running `nvidia-smi daemon` (root privilege required) will make the query much **faster**.
 - The GPU ID (index) shown by `gpustat` (and `nvidia-smi`) is PCI BUS ID,
   while CUDA differently assigns the fastest GPU with the lowest ID by default.

gpustat.py

@@ -23,13 +23,11 @@
 import pynvml as N
 from blessings import Terminal
 
-__version__ = '0.4.0.dev0'
+__version__ = '0.4.0.dev1'
 
 
 NOT_SUPPORTED = 'Not Supported'
 
-term = Terminal()
-
 
 class GPUStat(object):
 
@@ -124,11 +122,12 @@ def processes(self):
 
 
     def print_to(self, fp,
-                 with_colors=True,
+                 with_colors=True,    # deprecated arg
                  show_cmd=False,
                  show_user=False,
                  show_pid=False,
-                 gpuname_width=16
+                 gpuname_width=16,
+                 term=Terminal(),
                  ):
         # color settings
         colors = {}
@@ -322,17 +321,28 @@ def __repr__(self):
 
     # --- Printing Functions ---
 
-    def print_formatted(self, fp=sys.stdout, no_color=False,
+    def print_formatted(self, fp=sys.stdout, force_color=False, no_color=False,
                         show_cmd=False, show_user=False, show_pid=False,
                         gpuname_width=16,
                         ):
+        # ANSI color configuration
+        if force_color and no_color:
+            raise ValueError("--color and --no_color can't be used at the same time")
+
+        if force_color:
+            t_color = Terminal(kind='linux', force_styling=True)
+        elif no_color:
+            t_color = Terminal(force_styling=None)
+        else:
+            t_color = Terminal()   # auto, depending on isatty
+
         # header
         time_format = locale.nl_langinfo(locale.D_T_FMT)
+
         header_msg = '{t.bold_white}{hostname}{t.normal}  {timestr}'.format(**{
             'hostname' : self.hostname,
             'timestr' : self.query_time.strftime(time_format),
-            't' : term if not no_color \
-                       else Terminal(force_styling=None)
+            't' : t_color,
         })
 
         fp.write(header_msg)
@@ -342,11 +352,11 @@ def print_formatted(self, fp=sys.stdout, no_color=False,
         gpuname_width = max([gpuname_width] + [len(g.entry['name']) for g in self])
         for g in self:
             g.print_to(fp,
-                       with_colors=not no_color,
                        show_cmd=show_cmd,
                        show_user=show_user,
                        show_pid=show_pid,
-                       gpuname_width=gpuname_width)
+                       gpuname_width=gpuname_width,
+                       term=t_color)
             fp.write('\n')
 
         fp.flush()
@@ -407,8 +417,13 @@ def main():
     # arguments to gpustat
     import argparse
     parser = argparse.ArgumentParser()
-    parser.add_argument('--no-color', action='store_true',
+
+    parser_color = parser.add_mutually_exclusive_group()
+    parser_color.add_argument('--force-color', '--color', action='store_true',
+                        help='Force to output with colors')
+    parser_color.add_argument('--no-color', action='store_true',
                         help='Suppress colored output')
+
     parser.add_argument('-c', '--show-cmd', action='store_true',
                         help='Display cmd name of running process')
     parser.add_argument('-u', '--show-user', action='store_true',