Defining variables in a loop based on a dictionary

Question

I am converting DICOMs to PNGs with Python 3.x and Pydicom. There are occasional errors when reading DICOM header tags, causing the script to crash. Until now, I worked around it by using exceptions like below:

try: studyd = ds.StudyDate
except: studyd = ''
pass
...

This repetitive approach lengthens the code.

Unfortunately, I fail optimizing the code by defining a dictionary containing the Pydicom header and the target variable and looping through it. How could I do this with something like:

ds = pydicom.dcmread()
tags = { 'StudyDate': 'studyd', 'Modality': 'modal', 'PatientName': 'patname', etc.}
for key, val in tags.items():
...

Do you really need to define variables like that? Can't you use a dictionary to store the values instead? — rdas, Apr 12 '20 at 12:51
I would prefer a dictionary. Would like to make a loop that sets the "val" of my dictionary as variable name and the ds.DICOMTAG as its value. — Sebastian Tschauner, Apr 12 '20 at 12:59

score 0 · Accepted Answer · answered Apr 12 '20 at 13:05

0

Try this:

ds = pydicom.dcmread()
tags = { 'StudyDate': 'studyd', 'Modality': 'modal', 'PatientName': 'patname', etc.}
header_dict = dict()
for key, val in tags.items():
    header_dict[val] = getattr(ds, key)
print(header_dict)

Using the getattr to get the header value and storing it in a dict against the specified name

answered Apr 12 '20 at 13:05

rdas

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Great, this did the job! Is it OK to write the dictionary back with: "globals().update(header_dict)" – Sebastian Tschauner Apr 12 '20 at 13:18
Yes you can do that. But it's usually bad practice to create variables (specially global ones) dynamically like that. You'll also confuse your IDE since it won't know where those variables came from – rdas Apr 12 '20 at 13:21
Could you recommend a better way to establish the variables from the dictionary? – Sebastian Tschauner Apr 12 '20 at 13:24
You could just use the dictionary entry in place of the variable. Like `header_dict['studyd']` – rdas Apr 12 '20 at 13:31
Thank you! This helped me a lot. – Sebastian Tschauner Apr 12 '20 at 17:49

Defining variables in a loop based on a dictionary

1 Answers1