[Python] How to open file using argparse?

I want to open file for reading using argparse. In cmd it must look like: my_program.py /filepath

That's my try:

parser = argparse.ArgumentParser()
parser.add_argument('file', type = file)
args = parser.parse_args()


This gives me [edit: added later from comment by OP]:

parser.add_argument('file', type = file) NameError: name 'file' is not defined

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