[python] Matplotlib: "Unknown projection '3d'" error

I just installed matplotlib and am trying to run one of there example scripts. However I run into the error detailed below. What am I doing wrong?

from mpl_toolkits.mplot3d import axes3d
import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.gca(projection='3d')
X, Y, Z = axes3d.get_test_data(0.05)
cset = ax.contour(X, Y, Z, 16, extend3d=True)
ax.clabel(cset, fontsize=9, inline=1)

plt.show()

The error is

Traceback (most recent call last):
  File "<string>", line 245, in run_nodebug
  File "<module1>", line 5, in <module>
  File "C:\Python26\lib\site-packages\matplotlib\figure.py", line 945, in gca
    return self.add_subplot(111, **kwargs)
  File "C:\Python26\lib\site-packages\matplotlib\figure.py", line 677, in add_subplot
    projection_class = get_projection_class(projection)
  File "C:\Python26\lib\site-packages\matplotlib\projections\__init__.py", line 61, in get_projection_class
    raise ValueError("Unknown projection '%s'" % projection)
ValueError: Unknown projection '3d'

Import mplot3d whole to use "projection = '3d'".

Insert the command below in top of your script. It should run fine.

from mpl_toolkits import mplot3d

Just to add to Joe Kington's answer (not enough reputation for a comment) there is a good example of mixing 2d and 3d plots in the documentation at http://matplotlib.org/examples/mplot3d/mixed_subplots_demo.html which shows projection='3d' working in combination with the Axes3D import.

from mpl_toolkits.mplot3d import Axes3D
...
ax = fig.add_subplot(2, 1, 1)
...
ax = fig.add_subplot(2, 1, 2, projection='3d')

In fact as long as the Axes3D import is present the line

from mpl_toolkits.mplot3d import Axes3D
...
ax = fig.gca(projection='3d')

as used by the OP also works. (checked with matplotlib version 1.3.1)

Try this:

import matplotlib.pyplot as plt
import seaborn as sns
from mpl_toolkits.mplot3d import axes3d

fig=plt.figure(figsize=(16,12.5))
ax=fig.add_subplot(2,2,1,projection="3d")

a=ax.scatter(Dataframe['bedrooms'],Dataframe['bathrooms'],Dataframe['floors'])
plt.plot(a)

I encounter the same problem, and @Joe Kington and @bvanlew's answer solve my problem.

but I should add more infomation when you use pycharm and enable auto import.

when you format the code, the code from mpl_toolkits.mplot3d import Axes3D will auto remove by pycharm.

so, my solution is

from mpl_toolkits.mplot3d import Axes3D
Axes3D = Axes3D  # pycharm auto import
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

and it works well!