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How to check is something is a list or a dictionary or a string?

Hi,

How to check if something is a list or a dictionary or just a string?
Eg:

for item in self.__libVerDict.itervalues():
self.cbAnalysisLibVersion(END, item)
where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?
Thanks,
Rajat
Aug 29 '08 #1
  • viewed: 2607
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6 Replies
On Aug 29, 9:16*am, dudeja.ra...@gmail.com wrote:
Hi,

How to check if something is a list or a dictionary or just a string?
Eg:

for item in self.__libVerDict.itervalues():
* * * * * * self.cbAnalysisLibVersion(END, item)

where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?

Thanks,
Rajat
type() and probably you want to import the types library as well.

In [1]: import types

In [2]: a = {1: {}, False: [], 'yes': False, None: 'HELLO'}

In [3]: a.values()
Out[3]: [[], {}, False, 'HELLO']

In [4]: [type(item) for item in a.itervalues()]
Out[4]: [<type 'list'>, <type 'dict'>, <type 'bool'>, <type 'str'>]

In [6]: for item in a.itervalues():
...: if type(item) is types.BooleanType:
...: print "Boolean", item
...: elif type(item) is types.ListType:
...: print "List", item
...: elif type(item) is types.StringType:
...: print "String", item
...: else:
...: print "Some other type", type(item), ':', item
...:
...:
List []
Some other type <type 'dict': {}
Boolean False
String HELLO
Aug 29 '08 #2
On Aug 29, 12:16 pm, dudeja.ra...@gmail.com wrote:
Hi,

How to check if something is a list or a dictionary or just a string?
Eg:

for item in self.__libVerDict.itervalues():
self.cbAnalysisLibVersion(END, item)

where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?
if isinstance(item,basestring):
# it's a string
...
else: # it should be a list
# typically you don't have to check it explicitly;
# even if it's not a list, it will raise an exception later anyway
if you call a list-specific method
HTH,
George
Aug 29 '08 #3
George Sakkis wrote:
On Aug 29, 12:16 pm, dudeja.ra...@gmail.com wrote:
>Hi,

How to check if something is a list or a dictionary or just a string?
Eg:

for item in self.__libVerDict.itervalues():
self.cbAnalysisLibVersion(END, item)

where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?

if isinstance(item,basestring):
# it's a string
...
else: # it should be a list
# typically you don't have to check it explicitly;
# even if it's not a list, it will raise an exception later anyway
if you call a list-specific method
HTH,
George
For a bit more explanation see, for example,

http://evanjones.ca/python-utf8.html

(Quote)
Working With Unicode Strings

Thankfully, everything in Python is supposed to treat Unicode strings
identically to byte strings. However, you need to be careful in your own
code when testing to see if an object is a string. Do not do this:

if isinstance( s, str ): # BAD: Not true for Unicode strings!

Instead, use the generic string base class, basestring:

if isinstance( s, basestring ): # True for both Unicode and byte strings
Aug 30 '08 #4
But this changes with Python 3, right?

On Aug 30, 7:15*am, Ken Starks <stra...@lampsacos.demon.co.ukwrote:
George Sakkis wrote:
On Aug 29, 12:16 pm, dudeja.ra...@gmail.com wrote:
Hi,
How to check if something is a list or a dictionary or just a string?
Eg:
for item in self.__libVerDict.itervalues():
* * * * * * self.cbAnalysisLibVersion(END, item)
where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?
if isinstance(item,basestring):
* *# it's a string
* * ...
else: # it should be a list
* *# typically you don't have to check it explicitly;
* *# even if it's not a list, it will raise an exception later anyway
if you call a list-specific method
HTH,
George

For a bit more explanation see, for example,

http://evanjones.ca/python-utf8.html

(Quote)
Working With Unicode Strings

Thankfully, everything in Python is supposed to treat Unicode strings
identically to byte strings. However, you need to be careful in your own
code when testing to see if an object is a string. Do not do this:

if isinstance( s, str ): # BAD: Not true for Unicode strings!

Instead, use the generic string base class, basestring:

if isinstance( s, basestring ): # True for both Unicode and byte strings
Aug 30 '08 #5
josh logan wrote:
But this changes with Python 3, right?
right!

see
http://docs.python.org/dev/3.0/whatsnew/3.0.html

(quote)
Strings and Bytes

* There is only one string type; its name is str but its behavior
and implementation are like unicode in 2.x.
* The basestring superclass has been removed. The 2to3 tool
replaces every occurrence of basestring with str.
* PEP 3137: There is a new type, bytes, to represent binary data
(and encoded text, which is treated as binary data until you decide to
decode it). The str and bytes types cannot be mixed; you must always
explicitly convert between them, using the str.encode() (str -bytes)
or bytes.decode() (bytes -str) methods.
* All backslashes in raw strings are interpreted literally. This
means that Unicode escapes are not treated specially.

* PEP 3112: Bytes literals, e.g. b"abc", create bytes instances.
* PEP 3120: UTF-8 default source encoding.
* PEP 3131: Non-ASCII identifiers. (However, the standard library
remains ASCII-only with the exception of contributor names in comments.)
* PEP 3116: New I/O Implementation. The API is nearly 100%
backwards compatible, but completely reimplemented (currently mostly in
Python). Also, binary files use bytes instead of strings.
* The StringIO and cStringIO modules are gone. Instead, import
io.StringIO or io.BytesIO.
* '\U' and '\u' escapes in raw strings are not treated specially.

On Aug 30, 7:15 am, Ken Starks <stra...@lampsacos.demon.co.ukwrote:
>George Sakkis wrote:
>>On Aug 29, 12:16 pm, dudeja.ra...@gmail.com wrote:
Hi,
How to check if something is a list or a dictionary or just a string?
Eg:
for item in self.__libVerDict.itervalues():
self.cbAnalysisLibVersion(END, item)
where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?
if isinstance(item,basestring):
# it's a string
...
else: # it should be a list
# typically you don't have to check it explicitly;
# even if it's not a list, it will raise an exception later anyway
if you call a list-specific method
HTH,
George
For a bit more explanation see, for example,

http://evanjones.ca/python-utf8.html

(Quote)
Working With Unicode Strings

Thankfully, everything in Python is supposed to treat Unicode strings
identically to byte strings. However, you need to be careful in your own
code when testing to see if an object is a string. Do not do this:

if isinstance( s, str ): # BAD: Not true for Unicode strings!

Instead, use the generic string base class, basestring:

if isinstance( s, basestring ): # True for both Unicode and byte strings
Aug 30 '08 #6
du**********@gmail.com wrote:
Hi,

How to check if something is a list or a dictionary or just a string?
Eg:

for item in self.__libVerDict.itervalues():
self.cbAnalysisLibVersion(END, item)
where __libVerDict is a dictionary that holds values as strings or
lists. So now, when I iterate this dictionary I want to check whether
the item is a list or just a string?
Thanks,
Rajat
Are you sure that is what you want to do or do you want to make sure that
"something" is an iterable. What if someone passed in a generator or a class
instance that is iterable, do you really want to fail?

-Larry
Aug 30 '08 #7

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