Reading from Python dict if key might not be present

Question

I am very new to Python and parsing data.

I can pull an external JSON feed into a Python dictionary and iterate over the dictionary.

for r in results:      print r['key_name'] 

As I walk through the results returned, I am getting an error when a key does not have a value (a value may not always exist for a record). If I print the results, it shows as

'key_name': None, 'next_key':................. 

My code breaks on the error. How can I control for a key not having a value?

Any help will be greatly appreciated!

Brock

Answer 1

The preferred way, when applicable:

for r in results:      print r.get('key_name') 

this will simply print None if key_name is not a key in the dictionary. You can also have a different default value, just pass it as the second argument:

for r in results:      print r.get('key_name', 'Missing: key_name') 

If you want to do something different than using a default value (say, skip the printing completely when the key is absent), then you need a bit more structure, i.e., either:

for r in results:     if 'key_name' in r:         print r['key_name'] 

or

for r in results:     try: print r['key_name']     except KeyError: pass 

the second one can be faster (if it's reasonably rare than a key is missing), but the first one appears to be more natural for many people.