Description:
Using Sage special function

Additional info:
sagemath 6.7-3
python2 2.7.10-1

Steps to reproduce:
Running this script in python2:
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from sage.functions.special import elliptic_pi
print(elliptic_pi(1, pi/4, 1))
---
results in this error:
---
Setting permissions of DOT_SAGE directory so only you can read and write it.
Traceback (most recent call last):
File "solenoid_phase.py", line 8, in <module>
from sage.functions.special import elliptic_pi
File "/usr/lib/python2.7/site-packages/sage/functions/__init__.py", line 1, in <module>
import all
File "/usr/lib/python2.7/site-packages/sage/functions/all.py", line 1, in <module>
from piecewise import piecewise, Piecewise
File "/usr/lib/python2.7/site-packages/sage/functions/piecewise.py", line 71, in <module>
from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
File "/usr/lib/python2.7/site-packages/sage/rings/polynomial/polynomial_ring_constructor.py", line 38, in <module>
import sage.rings.padics.padic_base_leaves as padic_base_leaves
File "/usr/lib/python2.7/site-packages/sage/rings/padics/padic_base_leaves.py", line 191, in <module>
from generic_nodes import pAdicFieldBaseGeneric, \
File "/usr/lib/python2.7/site-packages/sage/rings/padics/generic_nodes.py", line 24, in <module>
from sage.rings.padics.local_generic import LocalGeneric
File "/usr/lib/python2.7/site-packages/sage/rings/padics/local_generic.py", line 26, in <module>
from sage.rings.integer import Integer
File "sage/rings/rational.pxd", line 10, in init sage.rings.integer (build/cythonized/sage/rings/integer.c:47210)
File "sage/rings/rational.pyx", line 59, in init sage.rings.rational (build/cythonized/sage/rings/rational.c:35590)
File "/usr/lib/python2.7/site-packages/sage/rings/rational_field.py", line 55, in <module>
import infinity
File "/usr/lib/python2.7/site-packages/sage/rings/infinity.py", line 219, in <module>
from sage.rings.integer_ring import ZZ
File "sage/rings/integer_ring.pyx", line 56, in init sage.rings.integer_ring (build/cythonized/sage/rings/integer_ring.c:14151)
File "/usr/lib/python2.7/site-packages/sage/rings/ideal.py", line 36, in <module>
from sage.interfaces.singular import singular as singular_default
File "/usr/lib/python2.7/site-packages/sage/interfaces/singular.py", line 336, in <module>
from expect import Expect, ExpectElement, FunctionElement, ExpectFunction
File "/usr/lib/python2.7/site-packages/sage/interfaces/expect.py", line 58, in <module>
import pexpect
ImportError: No module named pexpect
---