Turning @Tomerikoo's comment into an answer:

Use a list comprehension:

[o.name for o in l]

Note that this will not necessarily be more efficient than looping, but obviously more beautiful.

Python lists do have an index method. But it only finds values that are equal to the argument, not values that have an argument that matches your partial value.

There's really nothing in Python that finds partial-structure matches like this; you can search/filter/etc. on equality, or on a predicate function, but anything else you have to write yourself.

The easiest way to do this is with a loop. You can write it explicitly:

for index, element in enumerate(my_array):
    if element["extension"] == ".py":
        return index

… or in a comprehension:

return next(index for index, element in enumerate(array)
            if element["extension"] == ".py")

Alternatively, you can turn the matching into a function, and pass it to filter, or use it as a key function in a more complex higher-order function, but there doesn't seem to be any real advantage to that here.

And of course you can write your own indexOf-like function that matches partial structures if you want.

One strategy to identify bugs in this code is to remove all conditions in the if clause, then add them one by one and checking whether the result is as expected.

You use the function hasattr. This function checks whether an object has a specific attribute (member variable, e.g., data[0].segments). data[0], however, is a dict. Dicts don't have a member called segments. What you're looking for is whether the dict contains a key segments, which you can achieve with the in operator:

if "segments" in item:
    ...

Then, there's another issue in your code. item["segments"] is a list, so you must use integers to access its members. Therefore, you get the error

TypeError: list indices must be integers or slices, not str

This error points towards the statement seg_id in item["segments"]["id"]. You can solve this with a double for loop or set comprehension and set intersection:

set(filter_config["segment_ids"]) & {seg["id"] for seg in item["segments"]}

Sets are containers wherein each element is unique. The operator & computes the intersection of two sets, i.e., the set of elements that are in both sets. set(filter_config["segment_ids"]) converts your list of segment IDs (I assume, it's a list) into a set. The set comprehension {seg["id"] for seg in item["segments"]} creates a set containing each segment IDs from the segments in the current item. The set is evaluated as true in an if statement iff the set is not empty.

Then, you should get your desired result.

Again, when you have a complex expression that doesn't work as expected, try to break it down to simpler expressions and check whether they do what you expect. Especially when learning, you can use an interactive Python session to build complex commands step by step, e.g., adding more and more filters, until you get what you need.

I would probably use the getattr built-in function for this purpose.

>>> my_object.my_attribute = 5
>>> getattr(my_object, 'my_attribute')
5

To create the numpy array as you would want:

def get_attrs(obj, attributes):
    """Returns the requested attributes of an object as a separate list"""
    return [getattr(obj, attr) for attr in attributes]

attributes = ['a', 'b', 'c']
attributes_per_object = np.array([get_attrs(obj, attributes) for obj in all_objects])

You can use zip() function:

for zipped in zip(arr1.split(",") , arr2.split(",")):
    someDictionary[zipped[0]] = zipped[1]

zip() creates tuple for each pair of items in collections, then you map one to another. If your 'arrays' have diffrent length, you can use map():

a = [1,3,4]
b = [3,4]
print map(None, a, b)
[(1, 3), (3, 4), (4, None)]

You just have to add one more B[0]:

Slice_num = np.load("Slice_num.npy")
B = Slice_num[person][i, [1]]   =>   B: ['-207.500000'] , <class 'numpy.ndarray'>
B[0]

and use float to get the value:

float(B[0])

In Python, you don't have to declare a variable before using it.

The line:

protocolsFound = [num]

Is probably intended to create a list of size num, but you can either just create it as an empty list protocolsFound = [] and start filling it with .append(), or if you need to be able to access specific positions in the list, you can create a list with num empty positions like protocolsFound = [None for _ in range(num)]. This is rarely needed in well-written Python code, though.

attrs = [o.attr for o in objs] was the right code for making a list like the one you describe. Don't try to subclass list for this. Is there something you did not like about that snippet?