It's confusing that np.longlong and np.int64 are inconsistent on Linux x64, however their str are both <type 'numpy.int64'>.

np.int64 == np.longlong is True on Windows, False on Linux.
np.dtype(np.longlong).char is 'q' on Windows x64 and Linux x64.
np.dtype(np.int64).char is 'q' on Windows x64, 'l' on Linux x64.

I think the reason is that the C type long is 32 bits on Windows x64, but 64 bits on Linux x64.

In the file numpy/core/include/numpy/npy_common.h,

On Linux x64,
sizeof(long) == 64, so #define NPY_INT64 NPY_LONG  

On Windows x64,
sizeof(long) == 32, so #define NPY_INT64 NPY_LONGLONG

Reproducing code example:

import numpy as np
print ('np.int64', 'np.longlong')
print (np.int64)
print (np.longlong)
print (np.int64 == np.longlong)
print (str(np.int64) == str(np.longlong))

print ('np.dtype(np.int64).type', 'np.dtype(np.longlong).type')
print (np.dtype(np.int64).type, np.dtype(np.longlong).type)
print (np.dtype(np.int64).type == np.dtype(np.longlong).type)

print ('np.dtype(np.int64).char', 'np.dtype(np.longlong).char')
print (np.dtype(np.int64).char, np.dtype(np.longlong).char)
print (np.dtype(np.int64).char == np.dtype(np.longlong).char)

print ('np.dtype(np.int64).name', 'np.dtype(np.longlong).name')
print (np.dtype(np.int64).name, np.dtype(np.longlong).name)
print (np.dtype(np.int64).name == np.dtype(np.longlong).name)

Output on Arch Linux x64, python2 and python3

('np.int64', 'np.longlong')
<type 'numpy.int64'>
<type 'numpy.int64'>
False
True
('np.dtype(np.int64).type', 'np.dtype(np.longlong).type')
(<type 'numpy.int64'>, <type 'numpy.int64'>)
False
('np.dtype(np.int64).char', 'np.dtype(np.longlong).char')
('l', 'q')
False
('np.dtype(np.int64).name', 'np.dtype(np.longlong).name')
('int64', 'int64')
True

Output on Windows 7 x64, python3

np.int64 np.longlong
<class 'numpy.int64'>
<class 'numpy.int64'>
True
True
np.dtype(np.int64).type np.dtype(np.longlong).type
<class 'numpy.int64'> <class 'numpy.int64'>
True
np.dtype(np.int64).char np.dtype(np.longlong).char
q q
True
np.dtype(np.int64).name np.dtype(np.longlong).name
int64 int64
True

Error message:

Numpy/Python version information:

On Linux x64,
Python2: ('1.15.2', '2.7.15 (default, Jun 27 2018, 13:05:28) \n[GCC 8.1.1 20180531]')
Python3: 1.15.2 3.7.1 (default, Oct 22 2018, 10:41:28) [GCC 8.2.1 20180831]

On Windows x64, 1.14.5 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:59:51) [MSC v.1914 64 bit (AMD64)]