pydicom is a pure Python module for working with DICOM files. It was made for inspecting and modifying DICOM files in an easy "pythonic" way. The modifications can be written again to a new file. As a pure python package, it should run anywhere python runs without any other requirements.
Here is a short code sample from an interactive python session:
>>> import dicom
>>> plan.dir("setup") # get a list of tags with "setup" somewhere in the name
(0018, 5100) Patient Position CS: 'HFS'
(300a, 0182) Patient Setup Number IS: '1'
(300a, 01b2) Setup TechniqueDescription ST: ''
>>> plan.PatientSetups.PatientPosition = "HFP"
pydicom is not a DICOM server, and is not about viewing images. It is designed to let you manipulate data elements in a DICOM file with python code.
pydicom is released under the GPL license. See the license.txt file in the distribution for details.