I have a data structure that looks something like this:
someData = {"apple":{"taste":"not bad","colors":["red","yellow"]},
"banana":{"taste":"perfection","shape":"banana shaped"},
"some list":[6,5,3,2,4,6,7]}
and a list of keys which describes a path to some item in this structure
someList = ["apple","colors",2]
I already have a function getPath(path)
(see below) that is supposed to return a pointer to the selected object. It works fine for reading, but I get into trouble when trying to write
print(getPath(someList))
>> yellow
getPath(someList) = "green"
>> SyntaxError: can't assign to function call
a = getPath(someList)
a = "green"
print(getPath(someList))
>> "yellow"
Is there a way to make this work? Maybe like this:
someFunc(someList, "green")
print(getPath(someList))
>> green
This question looks like this question , except that I want to write something to that item, and not just read it.
My actual data can be seen here (I used json.loads() to parse the data). Note that I plan on adding stuff to this structure. I want a general approach to future proof the project.
My code:
def getPath(path):
nowSelection = jsonData
for i in path:
nowSelection = nowSelection[i]
return nowSelection
The result you're getting from getPath()
is the immutable value from a dict or list. This value does not even know it's stored in a dict or list, and there's nothing you can do to change it. You have to change the dict/list itself.
Example:
a = {'hello': [0, 1, 2], 'world': 2}
b = a['hello'][1]
b = 99 # a is completely unaffected by this
Compare with:
a = {'hello': [0, 1, 2], 'world': 2}
b = a['hello'] # b is a list, which you can change
b[1] = 99 # now a is {'hello': [0, 99, 2], 'world': 2}
In your case, instead of following the path all the way to the value you want, go all the way except the last step, and then modify the dict/list you get from the penultimate step:
getPath(["apple","colors",2]) = "green" # doesn't work
getPath(["apple","colors"])[2] = "green" # should work
You could cache your getPath
using custom caching function that allows you to manually populate saved cache.
from functools import wraps
def cached(func):
func.cache = {}
@wraps(func)
def wrapper(*args):
try:
return func.cache[args]
except KeyError:
func.cache[args] = result = func(*args)
return result
return wrapper
@cached
def getPath(l):
...
getPath.cache[(someList, )] = 'green'
getPath(someList) # -> 'green'
You can't literally do what you're trying to do. I think the closest you could get is to pass the new value in, then manually reassign it within the function:
someData = {"apple":{"taste":"not bad","colors":["red","yellow"]}, "banana":{"taste":"perfection","shape":"banana shaped"}, "some list":[6,5,3,2,4,6,7]}
def setPath(path, newElement):
nowSelection = someData
for i in path[:-1]: # Remove the last element of the path
nowSelection = nowSelection[i]
nowSelection[path[-1]] = newElement # Then use the last element here to do a reassignment
someList = ["apple","colors",1]
setPath(someList, "green")
print(someData)
{'apple': {'taste': 'not bad', 'colors': ['red', 'green']}, 'banana': {'taste': 'perfection', 'shape': 'banana shaped'}, 'some list': [6, 5, 3, 2, 4, 6, 7]}
I renamed it to setPath
to reflect its purpose better.
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