Bug with Sphinx extension in tutorial

[asmeurer]

At http://docs.sympy.org/latest/tutorial/basic_operations.html, if you run the block

>>> str_expr = "x**2 + 3*x - 1/2"
>>> expr = sympify(str_expr)
>>> expr
x**2 + 3*x - 1/2
>>> expr.subs(x, 2)
19/2

It runs as

>>> expr = sympify(str_expr)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'str_expr' is not defined
>>> expr
sin(x)
>>> expr.subs(x, 2)
sin(2)

and if you run

>>> import numpy 
>>> a = numpy.arange(10) 
>>> expr = sin(x)
>>> f = lambdify(x, expr, "numpy") 
>>> f(a) 
[ 0.          0.84147098  0.90929743  0.14112001 -0.7568025  -0.95892427
 -0.2794155   0.6569866   0.98935825  0.41211849]

it runs as

>>> a = numpy.arange(10)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'numpy' is not defined
>>> expr = sin(x)
>>> f = lambdify(x, expr, "numpy")
>>> f(a)
Traceback (most recent call last):
  File "<string>", line 1, in <module>
NameError: name 'a' is not defined

It's not running the first line for some reason.