[FIXED] Adding "sequential" information to python list using dictionaries

Issue

The problem

I would like to create a dictionary of dicts out of a flat list I have in order to add a "sequentiality" piece of information, but I am having some trouble finding a solution.

The list is something like

a = ['Q=123', 'W=456', 'E=789', 'Q=753', 'W=159', 'E=888']

and I am shooting for a dict like:

dictionary = {
    'Step_1': {
        'Q=123', 
        'W=456', 
        'E=789'
    },
    'Step_2': {
        'Q=753', 
        'W=159', 
        'E=888'
    }
}

I would like to end up with a function with an arbitrary number of Steps, in order to apply it to my dataset. Suppose that in the dataset there are lists like a with 1 <= n <6 Steps each.

My idea

Up to now, I came up with this:

nsteps = a.count("Q")
data = {}
for i in range(nsteps):
    stepi = {}
    for element in a:
            new = element.split("=")
            if new[0] not in stepi:
                stepi[new[0]] = new[1]
            else:
                pass
    data[f"Step_{i}"] = stepi

but it doesn't work as intended: both steps in the final dictionary contain the data of Step_1. Any idea on how to solve this?

Solution

One way would be:

a = ['Q=123', 'W=456', 'E=789', 'Q=753', 'W=159', 'E=888']

indices = [i for i, v in enumerate(a) if v[0:2] == 'Q=']

dictionary = {f'Step_{idx+1}': {k: v for k, v in (el.split('=') for el in a[s:e])} 
              for idx, (s, e) in enumerate(zip(indices, indices[1:] + [len(a)]))}

print(dictionary)

{'Step_1': {'Q': '123', 'W': '456', 'E': '789'}, 
'Step_2': {'Q': '753', 'W': '159', 'E': '888'}}

Details:

a = ['Q=123', 'W=456', 'E=789', 'Q=753', 'W=159', 'E=888']

# Get indices where a step starts. 
# This could handle also steps with variable amount of elements and keys starting with 'Q' that are not exactly 'Q'.
indices = [i for i, v in enumerate(a) if v[0:2] == 'Q=']

# Get the slices of the list starting at Q and ending before the next Q.
slices = list(zip(indices, indices[1:] + [len(a)]))
print(slices)
# [(0, 3), (3, 6)]

# Get step index and (start, end) pair for each slice.
idx_slices = list(enumerate(slices))
print(idx_slices)
# [(0, (0, 3)), (1, (3, 6))]

# Split the strings in the list slices and use the result as key-value pair for a given start:end.
# Here an example for step 1:
step1 = idx_slices[0][1] # This is (0, 3).
dict_step1 = {k: v for k, v in (el.split('=') for el in a[step1[0]:step1[1]])}
print(dict_step1)
# {'Q': '123', 'W': '456', 'E': '789'}

# Do the same for each slice.
step_dicts = {f'Step_{idx+1}': {k: v for k, v in (el.split('=') for el in a[s:e])}
              for idx, (s, e) in idx_slices}
print(step_dicts)
# {'Step_1': {'Q': '123', 'W': '456', 'E': '789'}, 'Step_2': {'Q': '753', 'W': '159', 'E': '888'}}

Answered By - user2246849