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I would like to be able to make a Python dictionary with strings as keys and sets of strings as the values. E.g.: { "crackers" : ["crunchy", "salty"] } It must be a set, not a list.
However, when I try the following:
word_dict = dict()
word_dict["foo"] = set()
word_dict["foo"] = word_dict["foo"].add("baz")
word_dict["foo"] = word_dict["foo"].add("bang")
I get:
Traceback (most recent call last):
File "process_input.py", line 56, in <module>
test()
File "process_input.py", line 51, in test
word_dict["foo"] = word_dict["foo"].add("bang")
AttributeError: 'NoneType' object has no attribute 'add'
If I do this:
word_dict = dict()
myset = set()
myset.add("bar")
word_dict["foo"] = myset
myset.add("bang")
word_dict["foo"] = myset
for key, value in word_dict:
print key,
print value
I get:
Traceback (most recent call last):
File "process_input.py", line 61, in <module>
test()
File "process_input.py", line 58, in test
for key, value in word_dict:
ValueError: too many values to unpack
Any tips on how to coerce Python into doing what I'd like? I'm an intermediate Python user (or so I thought, until I ran into this problem.)
988
We can also use the map() function to convert a list of strings to a list of numbers representing the length of each string element i.e. It iterates over the list of string and apply len() function on each string element. Then stores the length returned by len() in a new sequence for every element.
We can use the Python built-in function map() to apply a function to each item in an iterable (like a list or dictionary) and return a new iterator for retrieving the results. map() returns a map object (an iterator), which we can use in other parts of our program.
The Python list stores a collection of objects in an ordered sequence. In contrast, the dictionary stores objects in an unordered collection. However, dictionaries allow a program to access any member of the collection using a key – which can be a human-readable string.
To convert a Python string to a dictionary, use the json. loads() function. The json. loads() is a built-in Python function that converts a valid string to a dict.
set.add() does not return a new set, it modifies the set it is called on. Use it this way:
word_dict = dict()
word_dict["foo"] = set()
word_dict["foo"].add("baz")
word_dict["foo"].add("bang")
Also, if you use a for loop to iterate over a dict, you are iterating over the keys:
for key in word_dict:
print key, word_dict[key]
Alternatively you could iterate over word_dict.items() or word_dict.iteritems():
for key, value in word_dict.items():
print key, value
from collections import defaultdict
word_dict = defaultdict(set)
word_dict['banana'].add('yellow')
word_dict['banana'].add('brown')
word_dict['apple'].add('red')
word_dict['apple'].add('green')
for key,values in word_dict.iteritems():
print "%s: %s" % (key, values)
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