Can somebody explain this code ?
l3 = [ {'from': 55, 'till': 55, 'interest': 15}, ]
l4 = list( {'from': 55, 'till': 55, 'interest': 15}, )
print l3, type(l3)
print l4, type(l4)
OUTPUT:
[{'till': 55, 'from': 55, 'interest': 15}] <type 'list'>
['till', 'from', 'interest'] <type 'list'>
When you convert a dict object to a list, it only takes the keys.
However, if you surround it with square brackets, it keeps everything the same, it just makes it a list of dicts, with only one item in it.
>>> obj = {1: 2, 3: 4, 5: 6, 7: 8}
>>> list(obj)
[1, 3, 5, 7]
>>> [obj]
[{1: 2, 3: 4, 5: 6, 7: 8}]
>>>
This is because, when you loop over with a for loop, it only takes the keys as well:
>>> for k in obj:
... print k
...
1
3
5
7
>>>
But if you want to get the keys and the values, use .items():
>>> list(obj.items())
[(1, 2), (3, 4), (5, 6), (7, 8)]
>>>
Using a for loop:
>>> for k, v in obj.items():
... print k, v
...
1 2
3 4
5 6
7 8
>>>
However, when you type in list.__doc__, it gives you the same as [].__doc__:
>>> print list.__doc__
list() -> new list
list(sequence) -> new list initialized from sequence's items
>>>
>>> print [].__doc__
list() -> new list
list(sequence) -> new list initialized from sequence's items
>>>
Kind of misleading :)
__doc__ is class(list) attribute, no wonder its instances([]) have that too.The former just wraps the entire item in square brackets [], making it a one-item list:
>>> [{'foo': 1, 'bar': 2}]
[{'foo': 1, 'bar': 2}]
The latter iterates over the dictionary (getting keys) and produces a list out of them:
>>> list({'foo': 1, 'bar': 2})
['foo', 'bar']
list() might cause error such as, list(3). Only [3] can work.>>> help(list)
Help on class list in module __builtin__:
class list(object)
| list() -> new empty list
| list(iterable) -> new list initialized from iterable's items
In the first case the notation indicates you're creating a list with a dictionary as its object. The list is created empty and the dictionary is appended as an object.
In the second case you're calling the second form of the list constructor - "initialized from iterable's items". In a dictionary it's the keys that are iterable, so you get a list of the dictionary keys.
The list is a constructor that will take any basic sequence (so tuples, dictionaries, other lists, etc.) and can turn them into lists. Alternatively, you could make the lists with [] and it will make a list with all the things you put inside the brackets. You can actually accomplish the same things with list comprehension.
13 = [item for item in {'from': 55, 'till': 55, 'interest': 15}]
14 = list({'from': 55, 'till': 55, 'interest': 15})
listuses dict.keys() and the first one is a list of dicts.list()takes an iterable and returns the list.