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Creating and Accessing Dictionaries |
Here is an example of a simple dictionary definition:
idlist = {"Smith,Mary":"P12345", "Doe,John":"P12346",
"Jones,Charlie":"P12347", "Public,John":"P12348",
"Dobbs,Cindy":"P12349"}
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In this dictionary, the keys are the names of people, and the values are their patient IDs.
To access the value of an element of a dictionary, supply its key in brackets []:
idlist = {"Smith,Mary":"P12345", "Doe,John":"P12346",
"Jones,Charlie":"P12347", "Public,John":"P12348",
"Dobbs,Cindy":"P12349"}
patientid = idlist["Public,John"] # patientid is now "P12348"
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To add a new element to a dictionary, assign a value to a new key:
idlist = {"Smith,Mary":"P12345", "Doe,John":"P12346",
"Jones,Charlie":"P12347", "Public,John":"P12348",
"Dobbs,Cindy":"P12349"}
idlist["Baxter,Ted"] = "P12350"
# idlist is now
# {'Jones,Charlie': 'P12347', 'Baxter,Ted': 'P12350',
# 'Public,John': 'P12348', 'Smith,Mary': 'P12345',
# 'Dobbs,Cindy': 'P12349', 'Doe,John': 'P12346'}
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To update an element of a dictionary, assign a new value to its key:
idlist = {"Smith,Mary":"P12345", "Doe,John":"P12346",
"Jones,Charlie":"P12347", "Public,John":"P12348",
"Dobbs,Cindy":"P12349"}
idlist["Jones,Charlie"] = "P55555"
# idlist is now
# {'Smith,Mary': 'P12345', 'Jones,Charlie': 'P55555',
# 'Public,John': 'P12348', # 'Dobbs,Cindy': 'P12349',
# 'Doe,John': 'P12346'}
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To delete an element, use del():
idlist = {"Smith,Mary":"P12345", "Doe,John":"P12346",
"Jones,Charlie":"P12347", "Public,John":"P12348",
"Dobbs,Cindy":"P12349"}
del(idlist["Dobbs,Cindy"])
# idlist is now
# {'Smith,Mary': 'P12345', 'Jones,Charlie': 'P12347',
# 'Public,John': 'P12348', 'Doe,John': 'P12346'}
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To check whether a key has an element defined in a dictionary, use has_key():
idlist = {"Smith,Mary":"P12345", "Doe,John":"P12346",
"Jones,Charlie":"P12347", "Public,John":"P12348",
"Dobbs,Cindy":"P12349"}
if not idlist.has_key("Roe,Jane"):
print "Jane Roe's patient ID is not known"
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| If you try to access a non-existent element of a dictionary, Python generates an error. | ||
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