Group and Array repr performance

[alimanfoo]

Generating a repr for a group can currently be slow, for the quirky reason that the repr needs to decide if the chunk_store is different to the store in order to generate an extra line showing the chunk store if different, and this triggers a complete comparison of store contents if the store is a shelve. E.g.:

In [37]: %lprun -f zarr.hierarchy.Group.__repr__ repr(g)
Timer unit: 1e-06 s

Total time: 5.60861 s
File: /home/aliman/miniconda3/envs/biipy_20170126_py35/lib/python3.5/site-packages/zarr/hierarchy.py
Function: __repr__ at line 194

Line #      Hits         Time  Per Hit   % Time  Line Contents
==============================================================
   194                                               def __repr__(self):
   195                                           
   196                                                   # main line
   197         1           11     11.0      0.0          r = '%s(' % type(self).__name__
   198         1           28     28.0      0.0          r += self.name + ', '
   199         1       276958 276958.0      4.9          r += str(len(self))
   200         1            2      2.0      0.0          r += ')'
   201                                           
   202                                                   # members
   203         1       244629 244629.0      4.4          array_keys = list(self.array_keys())
   204         1            2      2.0      0.0          if array_keys:
   205         1            1      1.0      0.0              arrays_line = '\n  arrays: %s; %s' % \
   206         1            8      8.0      0.0                  (len(array_keys), ', '.join(array_keys))
   207         1            1      1.0      0.0              if len(arrays_line) > 80:
   208         1            1      1.0      0.0                  arrays_line = arrays_line[:77] + '...'
   209         1            1      1.0      0.0              r += arrays_line
   210         1       240623 240623.0      4.3          group_keys = list(self.group_keys())
   211         1            3      3.0      0.0          if group_keys:
   212                                                       groups_line = '\n  groups: %s; %s' % \
   213                                                           (len(group_keys), ', '.join(group_keys))
   214                                                       if len(groups_line) > 80:
   215                                                           groups_line = groups_line[:77] + '...'
   216                                                       r += groups_line
   217                                           
   218                                                   # storage and synchronizer classes
   219         1           10     10.0      0.0          r += '\n  store: %s' % type(self.store).__name__
   220         1      4846320 4846320.0     86.4          if self.store != self.chunk_store:
   221                                                       r += '; chunk_store: %s' % type(self.chunk_store).__name__
   222         1           13     13.0      0.0          if self.synchronizer is not None:
   223                                                       r += '; synchronizer: %s' % type(self.synchronizer).__name__
   224                                           
   225         1            1      1.0      0.0          return r

There should be a way to avoid this comparison, at least in the case where chunk_store is None when the Group is instantiated, because then it is known there is no separate chunk store.

[alimanfoo]

Also there are two pain points for Array.__repr__:

Timer unit: 1e-06 s

Total time: 9.77442 s
File: /home/aliman/miniconda3/envs/biipy_20170126_py35/lib/python3.5/site-packages/zarr/core.py
Function: _repr_nosync at line 816

Line #      Hits         Time  Per Hit   % Time  Line Contents
==============================================================
   816                                               def _repr_nosync(self):
   817                                           
   818                                                   # main line
   819         1           40     40.0      0.0          r = '%s(' % type(self).__name__
   820         1           19     19.0      0.0          if self.name:
   821         1           10     10.0      0.0              r += '%s, ' % self.name
   822         1           13     13.0      0.0          r += '%s, ' % str(self._shape)
   823         1            7      7.0      0.0          r += '%s, ' % str(self._dtype)
   824         1            6      6.0      0.0          r += 'chunks=%s, ' % str(self._chunks)
   825         1            4      4.0      0.0          r += 'order=%s' % self._order
   826         1            2      2.0      0.0          r += ')'
   827                                           
   828                                                   # storage size info
   829         1           42     42.0      0.0          r += '\n  nbytes: %s' % human_readable_size(self._nbytes)
   830         1      4854174 4854174.0     49.7          if self.nbytes_stored > 0:
   831                                                       r += '; nbytes_stored: %s' % human_readable_size(
   832                                                           self.nbytes_stored)
   833                                                       r += '; ratio: %.1f' % (self._nbytes / self.nbytes_stored)
   834         1       130277 130277.0      1.3          r += '; initialized: %s/%s' % (self.nchunks_initialized,
   835         1           33     33.0      0.0                                         self._nchunks)
   836                                           
   837                                                   # filters
   838         1            2      2.0      0.0          if self._filters:
   839                                                       # first line
   840                                                       r += '\n  filters: %r' % self._filters[0]
   841                                                       # subsequent lines
   842                                                       for f in self._filters[1:]:
   843                                                           r += '\n           %r' % f
   844                                           
   845                                                   # compressor
   846         1            1      1.0      0.0          if self._compressor:
   847         1           10     10.0      0.0              r += '\n  compressor: %r' % self._compressor
   848                                           
   849                                                   # storage and synchronizer classes
   850         1            2      2.0      0.0          r += '\n  store: %s' % type(self._store).__name__
   851         1      4789776 4789776.0     49.0          if self._store != self._chunk_store:
   852                                                       r += '; chunk_store: %s' % type(self._chunk_store).__name__
   853         1            4      4.0      0.0          if self._synchronizer is not None:
   854                                                       r += '; synchronizer: %s' % type(self._synchronizer).__name__
   855                                           

[alimanfoo]

Should be straightforward to fix, by setting _chunk_store attribute as None.