6. Files

6.1. Opening ROOT files with rootpy.io.root_open()

rootpy provides the rootpy.io.root_open() function that internally uses ROOT’s TFile::Open, but instead returns a rootpy.io.File object. For example:

>>> from rootpy.io import root_open
>>> myfile = root_open('some_file.root', 'recreate')
>>> myfile
>>> myfile.__class__.__bases__
(<class 'rootpy.io.file._DirectoryBase'>, <class 'ROOT.TFile'>)

Additionally, any objects retrieved from a rootpy File are automatically cast to the subclass in rootpy, if one exists:

>>> from rootpy.testdata import get_file
>>> testfile = get_file()
>>> myhist = testfile.dimensions.hist2d
>>> myhist

rootpy’s File class inherits from ROOT’s TFile but can additionally act as a context manager:

from rootpy.io import root_open

with root_open('some_file.root') as myfile:
    # the file is open in this context
    myhist = myfile.somedirectory.histname.Clone()
# when the context is left the file is closed

Also, as demonstrated in the example above, contents of files and directories can be accesses as attributes (myfile.somedirectory.histname).

6.2. Utilities

rootpy files can be “walked” in a similar way to Python’s os.walk():

from rootpy.testdata import get_file

# use the test file shipped with rootpy
with get_file() as f:
    # access objects by name as properties of the current dir
    myhist = f.dimensions.hist2d
    # recursively walk through the file
    for path, dirs, objects in f.walk():
        # do something
        print(path, dirs, objects)

the output of which is:

 ['dimensions', 'scales', 'means', 'graphs', 'gaps', 'efficiencies'] []
dimensions [] ['hist2d', 'hist3d']
scales [] ['hist1', 'hist3', 'hist2', 'hist4']
means [] ['hist1', 'hist3', 'hist2', 'hist4']
graphs [] ['tgrapherrors', 'tgraph2d', 'tgraphasymmerrors', 'tgraph']
gaps [] ['hist1', 'hist3', 'hist2', 'hist4']
efficiencies [] ['hist1', 'hist3', 'hist2', 'hist4', 'eff3v1', 'eff2v1', 'eff4v1']

Also see rootpy.io.

6.3. Temporary Files

rootpy provides a rootpy.io.TemporaryFile that when closed is automatically deleted from the filesystem. This may be useful when creating temporary objects, such as trees copied with a selection that are no longer needed after the termination of the program.