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A simple wrapper for the h5py library.

Project description

simple h5py

A simple wrapper for the h5py library

Publish to PyPI Publish to Conda

import numpy as np
from simple_h5py import BasicH5File

# Creating some data
# >> notice the "huge" attribute !
group_attrs = dict(a=1, b=2)
dataset = np.ones((5, 4, 3))
dataset_attrs = dict(new=5, huge=np.ones((1000000, 3)))

# Write contents to file
obj = BasicH5File('demo.h5')
obj['my_group'] = None
obj['my_group'].attrs = group_attrs.copy()
obj['my_group']['my_dataset'] = dataset
obj['my_group']['my_dataset'].attrs = dataset_attrs.copy()

# Read contents from file
obj = BasicH5File('demo.h5')

The above snippet creates a HDF5 file with the following "content tree".

│── my_group
│   ├── .attrs
│      ├── a (1)      └── b (2)   └── my_dataset (array)       └── .attrs
│           ├── new (5)           └── huge (array ref)
└── big_attrs
    └── my_group.my_dataset.attrs.huge (array)

See below for the equivalent snippet using vanilla h5py.


Installation instructions

From PyPI

pip install simple_h5py

From Conda

conda install -c arturo.mendoza.quispe simple_h5py

From git

pip install git+

Library Features

:rocket: Full Python experience

While h5py does provide a high-level interface to the HDF5 library using established Python and NumPy concepts, it purposely does not go the extra mile to provide a full Python experience to the user. Of course, this design choice allows for great flexibility such as enabling chunked storage, allowing to store and manipulate the data in memory (using the core driver) and much more !

The goal of simple_h5py is to allow easier creation and handling of HDF5 files using the fabulous h5py library as a support :+1:

The following example highlights the similarity between creating a python-only object and creating a HDF5 file using simple_h5py !

obj = dict()
obj['group'] = dict()
obj['group']['attrs'] = dict(a=1, b=2)
obj['group']['dataset'] = dict(contents=dataset)
obj['group']['dataset']['attrs'] = dict(c=3, d=4)

obj = BasicH5File('myfile.h5')
obj['group'] = None
obj['group'].attrs = dict(a=1, b=2)
obj['group']['dataset'] = dataset
obj['group']['dataset'].attrs = dict(c=3, d=4)

:zap: Intelligent open/close of file

If the library is used for creating a new HDF5 file, it will open the file stream whenever a new value is given (either to a group, a dataset or an attribute instance) and subsequently closes it. This is done only once for each __setitem__ call. Hence, setting an entire attribute group with a single dictionary will only require one open/close directive. However, setting each attribute group entry will require multiple ones.

It the library is used for reading a new HDF5 file, it will parse the complete content-tree and load it into memory. Additionally, it will load all group and dataset attributes too. However, the datasets will not be loaded since they are assumed to be heavy. Since the returned object contains the correct HDF5 references, the datasets can be loaded at any time (either completely or partially).

obj = BasicH5File('myfile.h5')           # Load content-tree & attrs from disk
v1 = obj['group'].attrs                  # Inspect object in memory
v2 = obj['group'].attrs['a']             # Inspect object in memory
v3 = obj['group']['dataset'].attrs       # Inspect object in memory
v4 = obj['group']['dataset'].attrs['c']  # Inspect object in memory
v5 = obj['group']['dataset'][:]          # Load complete dataset from disk
v6 = obj['group']['dataset'][:10]        # Partially load dataset from disk

This strategy should allow a more fluid interaction with the HDF5 file since it can be fully inspected at any time, without requiring multiple open/close directives !

:earth_americas: Handling of BIG ATTRIBUTES

The section of HDF5 User's Guide dedicated to the case of Large Attributes. Since, Attributes are intended to be small objects, most implementations limit the size of these meta-data (h5py will throw a RuntimeError). The User's Guide proposes to point the attribute to another supplemental dataset.

simple_h5py implements this and makes the issue completely transparent to the user. Every large attribute will be stored into a dataset with full path /big_attrs/<dataset_name>.<group_name>.attrs.<attribute_name>.

obj = BasicH5File('myfile.h5')
dst = obj['group']['dataset']
dst.attrs['e'] = np.ones((1000000, 3))  # silently creates large dataset in
                                        # '/big_attrs/group.dataset.attrs.e'
dst.attrs['f'] = np.ones((10, 3))       # normal attribute creation but with
                                        # identical syntax ! 

Note that simple_h5py automatically handles the huge attribute during both, reading and writing the contents !

obj = BasicH5File('myfile.h5')
v7 = obj['group']['dataset'].attrs['e']  # they are identical for the user !
v8 = obj['group']['dataset'].attrs['f']

:pencil2: Nice print of the content-tree

Since the BasicH5File contains the entire content-tree at all times, displaying the object (either __repr__ or __str__) allows for fast inspection of the file contents.

# BasicH5File (myfile.h5)
# > Group "/group"
#   > Dataset "/group/dataset" (20, 30, 10)

# Group
# > path: myfile.h5
# > route: /group
# > attrs: {'a': 1, 'b': 2}
# > datasets: ['dataset']

# Dataset
# > path: myfile.h5
# > route: /group/dataset
# > attrs: {'c': 3, 'd': 4, 'e': array([[1., 1., 1.],
#        ...,
#        [1., 1., 1.]]), 'f': array([[1., 1., 1.],
#        ...,
#        [1., 1., 1.]])}
# > shape: (20, 30, 10)

:cake: [EXTRA] Define required attributes

Define required attributes for all groups and all datasets:

obj = BasicH5File('myfile.h5',
                  group_attrs_required=('a', 'b'),
                  dataset_attrs_required=('c', 'd'))

As such, if a file does not comply, an assertion error is raised. A file may have more attributes than those required, but no less.

This feature is useful for ensuring that the HDF5 files to be read comply with the desired criteria. One can even subclass the BasicH5File for easier use:

class StrictH5File(BasicH5File):
    def __init__(self, path: str):
                         group_attrs_required=('a', 'b'),
                         dataset_attrs_required=('c', 'd'))

obj = StrictH5File('myfile.h5')

Additional notes

simple_h5py is not meant to be a h5py replacement but a useful sidekick. Indeed, for "simple" use-cases, such as those shown here, simple_h5py allows faster development by hiding many of the implementation details. As such, h5py should be employed for more advanced or custom needs. Moroever, a file can be written with simple_h5py and then be read using h5py, and viceversa.

Equivalent snippet using h5py

The following code performs has the same effect as the sample snippet.

Note the simpler syntax that allows simple_h5py !

import h5py
import numpy as np

group_attrs = dict(a=1, b=2)
dataset = np.ones((5, 4, 3))
dataset_attrs = dict(new=5, huge=np.ones((1000000, 3)))

# Use context manager to avoid open/close
with h5py.File('demo.h5', 'w') as obj:
    # Create group

    # Add attributes to group one at a time
    for k, v in group_attrs.items():
        obj['my_group'].attrs[k] = v

    # Create dataset
    obj['my_group'].create_dataset('my_dataset', data=dataset)

    # Add attributes to dataset one at a time
    for k, v in dataset_attrs.items():

        # Use try/except for capturing the "large attributes"
            obj['my_group']['my_dataset'].attrs[k] = v
        except BaseException:
            # Create an auxiliary dataset called in a helper group 'big_attrs'
            if 'big_attrs' not in obj:

            # Store the reference to the auxiliary dataset
            obj['my_group']['my_dataset'].attrs[k] = \

# Use context manager to avoid open/close
with h5py.File('demo.h5', 'r') as obj:

    # Read attributes and convert to dictionary for further use
    read_group_attrs = dict(obj['my_group'].attrs)
    read_dataset_attrs = dict(obj['my_group']['my_dataset'].attrs)

    # Read entire dataset
    read_dataset = obj['my_group']['my_dataset'][:]

    # Verify if any reference is present in the attributes (i.e. big attribute)
    for k, v in read_dataset_attrs.items():
        if isinstance(v, h5py.Reference):
            read_dataset_attrs[k] = obj[v][:]

# Display contents

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