use plt.subplots() in examples as much as possible

At the recent LBL Software Carpentry Workshop, it was pointed out that there's
an inconsistency within our documentation for how to create new figures with
subplots.

Indeed, most examples were using the old way, something like:

    fig = plt.figure()
    ax = plt.subplot(111) # or plt.add_subplot(111)

This patch changes a whole bunch of instances like the above to:

    fig, ax = plt.subplots()

We should strive to have a minimal amount of constants in our code,
especially unusual ones like `111`, which only make sense to Matlab
refugees.

I have left unchanged examples which were using axes keywords passed to
subplot() and add_subplot(), since those end up transforming things like:

    figure()
    subplot(111, axisbg='w')

to

    plt.subplots(subplot_kw=dict(axisbg='w'))

which isn't necessarily better.

I also did not touch most of the user_interfaces examples, since those did not
involve using plt, but instead explicitly imported Figure, and used the OO
approach on Figure instances.

Also updated instaces where the old "import pylab as p" convention was used to
use our standard "import matplotlib.pyplot as plt"

I have also updated some, but not all uses of subplot(121) etc, but I'm a bit
exhausted after doing all of these.

Author: ivanov

CHANGELOG

@@ -90,6 +90,10 @@
 
 2012-11-09 Make plt.subplot() without arguments act as subplot(111) - PI
 
+2012-11-08 Replaced plt.figure and plt.subplot calls by the newer, more
+           convenient single call to plt.subplots() in the documentation
+           examples - PI
+
 2012-10-05 Add support for saving animations as animated GIFs. - JVDP
 
 2012-08-11 Fix path-closing bug in patches.Polygon, so that regardless

examples/animation/animate_decay.py

@@ -11,8 +11,7 @@ def data_gen():
         yield t, np.sin(2*np.pi*t) * np.exp(-t/10.)
 data_gen.t = 0
 
-fig = plt.figure()
-ax = fig.add_subplot(111)
+fig, ax = plt.subplots()
 line, = ax.plot([], [], lw=2)
 ax.set_ylim(-1.1, 1.1)
 ax.set_xlim(0, 5)

examples/animation/histogram.py

@@ -9,8 +9,7 @@
 import matplotlib.path as path
 import matplotlib.animation as animation
 
-fig = plt.figure()
-ax = fig.add_subplot(111)
+fig, ax = plt.subplots()
 
 # histogram our data with numpy
 data = np.random.randn(1000)

examples/animation/old_animation/animate_decay_tk_blit.py

@@ -10,8 +10,7 @@ def data_gen():
     return np.sin(2*np.pi*t) * np.exp(-t/10.)
 data_gen.t = 0
 
-fig = plt.figure()
-ax = fig.add_subplot(111)
+fig, ax = plt.subplots()
 line, = ax.plot([], [], animated=True, lw=2)
 ax.set_ylim(-1.1, 1.1)
 ax.set_xlim(0, 5)

examples/animation/old_animation/animation_blit_gtk.py

@@ -16,8 +16,7 @@
 import matplotlib.pyplot as plt
 
 
-fig = plt.figure()
-ax = fig.add_subplot(111)
+fig, ax = plt.subplots()
 canvas = fig.canvas
 
 fig.subplots_adjust(left=0.3, bottom=0.3) # check for flipy bugs

examples/animation/old_animation/animation_blit_gtk2.py

@@ -148,9 +148,8 @@ def update_line(self, *args):
 
 
 plt.rcParams["text.usetex"] = False
-fig = plt.figure()
 
-ax = fig.add_subplot(111)
+fig, ax = plt.subplots()
 ax.xaxis.set_animated(True)
 ax.yaxis.set_animated(True)
 canvas = fig.canvas

examples/animation/old_animation/animation_blit_tk.py

@@ -7,17 +7,17 @@
 matplotlib.use('TkAgg')
 
 import sys
-import pylab as p
+import matplotlib.pyplot as plt
 import numpy as npy
 import time
 
-ax = p.subplot(111)
+fig, ax = plt.subplots()
 canvas = ax.figure.canvas
 
 
 # create the initial line
 x = npy.arange(0,2*npy.pi,0.01)
-line, = p.plot(x, npy.sin(x), animated=True, lw=2)
+line, = plt.plot(x, npy.sin(x), animated=True, lw=2)
 
 def run(*args):
     background = canvas.copy_from_bbox(ax.bbox)
@@ -43,12 +43,12 @@ def run(*args):
 run.cnt = 0
 
 
-p.subplots_adjust(left=0.3, bottom=0.3) # check for flipy bugs
-p.grid() # to ensure proper background restore
-manager = p.get_current_fig_manager()
+plt.subplots_adjust(left=0.3, bottom=0.3) # check for flipy bugs
+plt.grid() # to ensure proper background restore
+manager = plt.get_current_fig_manager()
 manager.window.after(100, run)
 
-p.show()
+plt.show()
 
 
 

examples/animation/old_animation/animation_blit_wx.py

@@ -24,7 +24,7 @@
     matplotlib.backends.backend_wxagg._use_accelerator(False)
 
 
-ax = p.subplot(111)
+fig, ax = plt.subplots()
 canvas = ax.figure.canvas
 
 

examples/animation/old_animation/draggable_legend.py

@@ -1,13 +1,12 @@
 import matplotlib.pyplot as plt
 
-
-ax = plt.subplot(111)
+fig, ax = plt.subplots()
 ax.plot([1,2,3], label="test")
 
 l = ax.legend()
 d1 = l.draggable()
 
-xy = 1, 2        
+xy = 1, 2
 txt = ax.annotate("Test", xy, xytext=(-30, 30),
                   textcoords="offset points",
                   bbox=dict(boxstyle="round",fc=(0.2, 1, 1)),

examples/animation/old_animation/gtk_timeout.py

@@ -5,8 +5,7 @@
 
 import matplotlib.pyplot as plt
 
-fig = plt.figure()
-ax = fig.add_subplot(111)
+fig, ax = plt.subplots()
 line, = ax.plot(np.random.rand(10))
 ax.set_ylim(0, 1)