Question

Task (Python)

A lot of police investigations start off by examining where the potential suspects

was at the time of the crime. This is often done by asking phone companies to

provide lists of all mobile phones that was in the area where the crime was

committed around the time when it was committed. If there is only one crime scene

this is not a big problem but if there are several crime scenes then the task of cross

referencing the lists gets quite tedious. To combat this the local police department

has decided to automate the process by creating a script that automatically does

most of the work for them.

The script shall work as follows:

1- Start the script

2- Provide one or more paths to files with phone numbers

3- The script finds out what phone numbers occur in all files

4- The script looks up who owns the phone numbers found

5- The script displays the found names

To break it all down a little bit further this is what should happen during each step.

1. When starting the script, a path to a file that contains the

mapping between name and number shall be given as a

command line argument. This file shall contain a pickled

dictionary on the following format {‘0709-12345’: ‘Anna’}.

2. To be able to provide an arbitrary number of files a menu is

needed. The menu shall have the following options: 1. Add

file and 2. Calculate. All file paths added shall be saved in a list

for later use.

3. This step is part of the menu option 2. Calculate. The script

shall cross reference the numbers in all the files provided and

create a Set with the ones that occur in all files. The files with

the phone numbers store one phone number per line and is

saved as a regular text file.

4. This step is part of the menu option 2. Calculate. Using the Set

of found numbers the script looks up the owner’s names using

the file sent as a command line argument. The names shall be

saved in a list.

5. All the found names located in the set from Step 4 is displayed

on the screen.

To solve task the student must make use of a main function and also implement the

following functions:

display_menu ()

This function shall display the following menu on screen:

1. Add file

2. Calculate

cross_reference (files)

The parameter files shall be a list of filenames (full path). The files shall be files

containing one phone number per line. The function shall create, and return,

a Set containing all the phone numbers that occurs in all files.

map_numbers_to_names (numbers, filename)

This function shall match each number from the Set numbers to a name and store

the names in a list. To accomplish this, the function shall use a dictionary that is

loaded (using pickle) from the file filename. The dictionary shall use the format

{‘0709-12345’: ‘Anna Karlsson’}. If a number can not be found in the dictionary it

shall be listed as Unknown with the phone number attached, like can be seen in this

example: Unknown (0709-11111). The function shall return the list with the names

and/or unknown tags.

display_suspects (names)

As the name of the function suggests this function shall display the names of all

suspects sent to the function as a list of strings. The format shall be as shown here:

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The following persons was present on all crime scenes:

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Max Olsson

Zara Walthersson

Unknown (0703-23464)

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If the list sent as a parameter is empty the following message shall be shown:

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The following persons was present on all crime scenes:

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No matches

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Make sure to include error handling that displays the following message to the user

if the file given as command line arguments or the files specified while running the

script is not valid:

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Error: There was a problem with at least one of the files.

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Hint: These files (owners, crime scene 1 , crime scene 2 and crime scene 3) and can be used     as an example of how the files with owner mapped to phone

numbers and the lists from the crime scenes might look like.