I have a dictionary "metadata" that contains key-value pairs of strings, lists, dicts, and integers. How can I loop through this dictionary and convert all values that are not of type string or integer to string?
Is there any way to simultaneously remove keys for which the value is empty? How could I do this without adding an additional loop?
Use isinstance to check the type of a value. In Python 3, you can simply write:
{k:v if isinstance(v, (str, int)) else str(v) for k,v in dct.items() if k != ''}
In older Python versions, you must be aware that there are no dictionary comprehensions (<2.7), and that there are multiple types that could be built-in ints and strings(<3). If you mean character strings when you talk about strings, the 2.5-2.7 equivalent would be
dict((k, v if isinstance(v, (unicode, int, long)) else unicode(v))
for k,v in dct.iteritems())
isinstance vs type?
isinstance will match subclasses. For example, if someone chooses to implement OptimizedString with a string that's faster than Python's built-in one (say, because they always know the encoding in their application, or the string is connected to network processing, or shared with TCL, etc.), this will still work. numpy's integer types are still valid ints. Checking with type(v) in ... would miss these subclasses.This works:
d={'l':[1,2,3],'s':'abc','i':5,'f':1.23,'di':{1:'one',2:'two'},'emty':''}
{k:v if type(v) in (str,int, long,unicode) else repr(v) for k,v in d.items() if v!=''}
Prints:
{'i': 5, 's': 'abc', 'di': "{1: 'one', 2: 'two'}", 'l': '[1, 2, 3]', 'f': '1.23'}
repr, which won't leave ints alone, and adds an extra quote to the strings (e.g. "abc" becomes "'abc'"). And if v will remove any 0 integers.
isinstancefunction.