.mat文件的读取与报错总结

最近使用一组mat格式的数据，在读取到一半类别数据时报错。一开始以为是数据损坏，经MATLAB查看，排除了该问题。后来分析和查错发现，是由于数据本身采用了不同版本的MATLAB保存，导致读取的时候出了一些问题。现总结两种不同的mat文件读取方式与错误读取时的报错，与大家分享，不足之处欢迎指正。

1. MATLAB v7.3 的mat文件使用h5py读取

示例：

import h5py

f = h5py.File('a.mat')
#　查看mat文件中的所有keys
list(f.keys()) 	
#　此处‘ａ’对应的value为三维，print后显示所有value; 注意，如果是data f['a']，print后显示文件类型和模式
data = f['a'][:,:,:]	
print(data)

若该类型的mat文件使用sicpy.io.loadmat读取，将会报错类似如下形式：

Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/local/lib/python3.5/dist-packages/scipy/io/matlab/mio.py", line 207, in loadmat
    MR, file_opened = mat_reader_factory(file_name, appendmat, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/scipy/io/matlab/mio.py", line 69, in mat_reader_factory
    raise NotImplementedError('Please use HDF reader for matlab v7.3 files')
NotImplementedError: Please use HDF reader for matlab v7.3 files

2. 其他版本mat文件可尝试使用scipy.io.loadmat
示例：

import scipy.io as scio

f = scio.loadmat('/home/dell/Way.mat')	# data同样为字典格式
print(f['C16'])	#打印key为C16的value

若该类型用h5py读取，可能报错如下：

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/h5py/_hl/files.py", line 190, in make_fid
    fid = h5f.open(name, h5f.ACC_RDWR, fapl=fapl)
  File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper
  File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper
  File "h5py/h5f.pyx", line 85, in h5py.h5f.open
OSError: Unable to open file (file signature not found)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/h5py/_hl/files.py", line 193, in make_fid
    fid = h5f.open(name, h5f.ACC_RDONLY, fapl=fapl)
  File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper
  File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper
  File "h5py/h5f.pyx", line 85, in h5py.h5f.open
OSError: Unable to open file (file signature not found)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/local/lib/python3.5/dist-packages/h5py/_hl/files.py", line 394, in __init__
    swmr=swmr)
  File "/usr/local/lib/python3.5/dist-packages/h5py/_hl/files.py", line 195, in make_fid
    fid = h5f.create(name, h5f.ACC_EXCL, fapl=fapl, fcpl=fcpl)
  File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper
  File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper
  File "h5py/h5f.pyx", line 105, in h5py.h5f.create
OSError: Unable to create file (unable to open file: name = '/home/dell/zhou/GAN-MSTAR/land_data/C17_HighWay.mat', errno = 17, error message = 'File exists', flags = 15, o_flags = c2)

３. 总结
使用数据前，先确定数据的类型、格式，避免走弯路。

参考资料：
https://github.com/h5py/h5py/issues/757
https://docs.scipy.org/doc/scipy-0.19.0/reference/generated/scipy.io.loadmat.html