ValueError: numpy.dtype has the wrong size, try recompiling

Question

I just installed pandas and statsmodels package on my python 2.7 When I tried "import pandas as pd", this error message comes out. Can anyone help? Thanks!!!

numpy.dtype has the wrong size, try recompiling
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\analytics\ext\python27\lib\site-packages\statsmodels-0.5.0-py2.7-win32.egg\statsmodels\formula\__init__.py",
line 4, in <module>
    from formulatools import handle_formula_data
  File "C:\analytics\ext\python27\lib\site-packages\statsmodels-0.5.0-py2.7-win32.egg\statsmodels\formula\formulatools.p
y", line 1, in <module>
    import statsmodels.tools.data as data_util
  File "C:\analytics\ext\python27\lib\site-packages\statsmodels-0.5.0-py2.7-win32.egg\statsmodels\tools\__init__.py", li
ne 1, in <module>
    from tools import add_constant, categorical
  File "C:\analytics\ext\python27\lib\site-packages\statsmodels-0.5.0-py2.7-win32.egg\statsmodels\tools\tools.py", line
14, in <module>
    from pandas import DataFrame
  File "C:\analytics\ext\python27\lib\site-packages\pandas\__init__.py", line 6, in <module>
    from . import hashtable, tslib, lib
  File "numpy.pxd", line 157, in init pandas.tslib (pandas\tslib.c:49133)
ValueError: numpy.dtype has the wrong size, try recompiling

Answer 1

(to expand a bit on my comment)

Numpy developers follow in general a policy of keeping a backward compatible binary interface (ABI). However, the ABI is not forward compatible.

What that means:

A package, that uses numpy in a compiled extension, is compiled against a specific version of numpy. Future version of numpy will be compatible with the compiled extension of the package (for exception see below). Distributers of those other packages do not need to recompile their package against a newer versions of numpy and users do not need to update these other packages, when users update to a newer version of numpy.

However, this does not go in the other direction. If a package is compiled against a specific numpy version, say 1.7, then there is no guarantee that the binaries of that package will work with older numpy versions, say 1.6, and very often or most of the time they will not.

The binary distribution of packages like pandas and statsmodels, that are compiled against a recent version of numpy, will not work when an older version of numpy is installed. Some packages, for example matplotlib, if I remember correctly, compile their extensions against the oldest numpy version that they support. In this case, users with the same old or any more recent version of numpy can use those binaries.

The error message in the question is a typical result of binary incompatibilities.

The solution is to get a binary compatible version, either by updating numpy to at least the version against which pandas or statsmodels were compiled, or to recompile pandas and statsmodels against the older version of numpy that is already installed.

Breaking the ABI backward compatibility:

Sometimes improvements or refactorings in numpy break ABI backward compatibility. This happened (unintentionally) with numpy 1.4.0. As a consequence, users that updated numpy to 1.4.0, had binary incompatibilities with all other compiled packages, that were compiled against a previous version of numpy. This requires that all packages with binary extensions that use numpy have to be recompiled to work with the ABI incompatible version.