PrintAfter this excursion into the realm of package management and package managers, let's come back to the previous topics covered in this lesson (list comprehension, web access, GUI development) and wrap up the lesson with a few practice exercises. These are meant to give you the opportunity to test how well you have understood the main concepts from this lesson and as a preparation for the homework assignment in which you are supposed to develop a small standalone and GUI-based program for a relatively simple GIS workflow using arcpy. Even if you don't manage to implement perfect solutions for all three exercises yourself, thinking about them and then carefully studying the provided solutions will be helpful, in particular since reading and understanding other people's code is an important skill and one of the main ways to become a better programmer. The solutions to the three practice exercises can be found in the following subsections.
Practice Exercise 1: List Comprehension
You have a list that contains dictionaries describing spatial features, e.g. obtained from some web service. Each dictionary stores the id, latitude, and longitude of the feature, all as strings, under the respective keys "id", "lat", and "lon":
features = [ { "id": "A", "lat": "23.32", "lon": "-54.22" },
{ "id": "B", "lat": "24.39", "lon": "53.11" },
{ "id": "C", "lat": "27.98", "lon": "-54.01" } ]
We want to convert this list into a list of 3-tuples instead using a list comprehension (Section 2.2). The first element of each tuple should be the id but with the fixed string "Feature " as prefix (e.g. "Feature A"). The other two elements should be the lat and lon coordinates but as floats not as strings. Here is an example of the kind of tuple we are looking for, namely the one for the first feature from the list above: ('Feature A', 23.32, -54.22). Moreover, only features with a longitude coordinate < 0 should appear in the new list. How would you achieve this task with a single list comprehension?