Databases Reference
In-Depth Information
>>>
path
in
grp
True
Multilevel Iteration with the Visitor Pattern
Basic iteration works fine for the contents of a single group. But what if you want to
iterate over every single object in the file? Or all objects “below” a certain group?
In the HDF5 world, this is accomplished by
visitor
iteration. Rather than HDF5 sup‐
plying you with an iterable, you provide a
callable
and HDF5 calls it with an argument
or two for every object.
Visit by Name
Your entry point is the
visit
method on the
Group
class. Let's create a simple file to test
it out:
>>>
f
=
h5py
.
File
(
'visit_test.hdf5'
,
'w'
)
>>>
f
.
create_dataset
(
'top_dataset'
,
data
=
1.0
)
>>>
f
.
create_group
(
'top_group_1'
)
>>>
f
.
create_group
(
'top_group_1/subgroup_1'
)
>>>
f
.
create_dataset
(
'top_group_1/subgroup_1/sub_dataset_1'
,
data
=
1.0
)
>>>
f
.
create_group
(
'top_group_2'
)
>>>
f
.
create_dataset
(
'top_group_2/sub_dataset_2'
,
data
=
1.0
)
We can supply any callable to
visit
, which takes one argument, the object name:
>>>
def
printname
(
name
):
...
print
name
>>>
f
.
visit
(
printname
)
top_dataset
top_group_1
top_group_1/subgroup_1
top_group_1/subgroup_1/sub_dataset_1
top_group_2
top_group_2/sub_dataset_2
No particular order is guaranteed, except that when
visit
enters a subgroup, all the
members will be visited before moving on to the next subgroup. For example, everything
under
top_group_1
is listed together, and so is everything under
top_group_2
.
You're not required to visit the entire file;
visit
works just fine on subgroups:
>>>
grp
=
f
[
'top_group_1'
]
>>>
grp
.
visit
(
printname
)
subgroup_1
subgroup_1/sub_dataset_1
