This question already has answers here:
How do you convert a stringed dictionary to a Python dictionary? [duplicate]
(3 answers)
Closed 8 years ago.
I got a string, it's like:
"{'a': 1, 'b': 2, 'c': 3}"
I want to assign a variable to this string and make the variable a dict.
It sounds easy, but I spend half hour and didn't figure it out. How to do it?
Use the ast.literal_eval() function as follows:
>>> import ast
>>> ast.literal_eval("{'a': 1, 'b': 2, 'c': 3}")
{'a': 1, 'b': 2, 'c': 3}
You could use it in a programme as follows:
import ast
dictString = "{'a': 1, 'b': 2, 'c': 3}";
dictFinal = ast.literal_eval(dictString)
print (dictFinal)
There is more help in the docs at this link
Related
This question already has answers here:
Does Python have an ordered set?
(15 answers)
Closed 3 years ago.
Is there a way of ordering a set in base python?
For example:
A = {1, 2, 3}
B = {3, -6, 2, 0}
print union(A, B)
Expected Output:
({-6, 0, 1, 2, 3}, 5)
My attempt:
x = A | B
y = len(x)
print((set(x), y))
My output:
({0, 1, 2, 3, -6}, 5)
I have read some of the answers for other questions and there are ways of doing it with various packages, but for this exercise, I am NOT meant to import any packages, just doing it in base python (if that is what it is called) if possible.
No, sets are unordered by definition and implementation. To create a sorted list, convert your set to a list and sort it:
List = sorted(your_set)
This question already has an answer here:
Create dictionary comprehension from list with condition syntax
(1 answer)
Closed 4 years ago.
I need to create a multiset tracking the frequencies of characters appearing in a given string. I wanted to implement this using dict comprehensions, but what I tried:
mySet = {letter : mySet.get(letter, 0) + 1 for letter in myStr}
Did not seem to work... as mySet.get(letter, 0) always seems to return 0. Is there another way to accomplish this simple task without resorting to loops?
Try Counter
from collections import Counter
Counter('Hello World')
This returns
Counter({' ': 1, 'H': 1, 'W': 1, 'd': 1, 'e': 1, 'l': 3, 'o': 2, 'r': 1})
This question already has answers here:
How can I get list of values from dict?
(7 answers)
Closed 5 years ago.
I want to extract the values from a dictionary and print them as a list. For example: If i have
letter = {"i": 3, "o": 2, "u": 2}
and want to extract 3,2, and 2 and print it as a list
[3, 2, 2]
How do I do this?
I've tried
print([x[::] for x in letter])
However, this prints out ['i', 'o', 'u'] and not [3, 2, 2].
Thank you for the help in advanced :)
There is a method in Python called .keys() that allows you to get the keys from a dict. Similarly, there is also a method called values() for the converse.
These are dict instance methods, ie:
myDict = { "i": 0, "t": 1, "f": 2 }
print(myDict.values())
You can just call dict.values()
Further details here
Try letter.values(), which gives you dict_values([3, 2, 2])
>>> letter = {"i": 3, "o": 2, "u": 2}
>>> print(list(letter.values()))
[3, 2, 2]
Example:
>>> x = {'a' : 3, 'b' : 5, 'c' : 6}
>>> x['d'] = x
>>> x
{'a': 3, 'b': 5, 'c': 6, 'd': {...}}
>>> x['d']
{'a': 3, 'b': 5, 'c': 6, 'd': {...}}
>>> x['d']['d']
{'a': 3, 'b': 5, 'c': 6, 'd': {...}}
>>> x['d']['d']['d']
{'a': 3, 'b': 5, 'c': 6, 'd': {...}}
I guess it is infinitely looped since it is referencing itself. I just wanted to know if there is any use case for such dictionaries in real world? If yes, any examples?
No actually I don't think that's a very useful thing. The author's opinion even leans the other way that it's hard enough to have objects copied in all the right spots in python.
One obvious possibility would be to subclass dict and create (or interface) an RPG like Nethack inside the python CLI that way. You could even add some sort of UI to it. Basically, dictionaries and other mapping types are "useful enough" in python without recursion, though.
This question already has answers here:
Order of keys in dictionary
(3 answers)
Closed 7 years ago.
I have two lists which I'm mapping into a dictionary.
The two lists are-
a = ['a','b','c','d'] and b = [1,2,3,4] .
When I run the command
>>> d = dict(zip(a,b))
>>> d
I get
{'a': 1, 'c': 3, 'b': 2, 'd': 4}
whereas the expected value is {'a': 1, 'b': 2, 'c': 3, 'd': 4}
Why this change in the order of the keys?
There is no inherent "obvious" order in the keys of a dict. Admittedly, the docs only spell it out for CPython, but also note
If items(), keys(), values(), iteritems(), iterkeys(), and
itervalues() are called with no intervening modifications to the
dictionary, the lists will directly correspond.
which says by omission that otherwise they might change.
(Note that there is an order, but it involves the hashes of the keys, so it's not as easy as "a before b", and in particular, since a few years back, it is liable to change with each new call of the executable.)
There is no order in a dictionary.
{'a': 1, 'b': 2, 'c': 3, 'd': 4} == {'a': 1, 'c': 3, 'b': 2, 'd': 4}