Chapter 2, Debugging and Profiling Python Scripts

1. To debug the program, the pdb module is used.

2. a) Before running ipython3, install using sudo apt-get install ipython3.
   b) %lsmagic.
3. A global interpreter lock is a mechanism used in computer language interpreters to synchronize the execution of threads so that only one native thread can execute at a time
4. Following are the answers:

a) PYTHONPATH: It has a role similar to PATH. This variable tells the Python interpreter where to locate the module files imported into a program. It should include the Python source library directory and the directories containing Python source code. PYTHONPATH is sometimes preset by the Python installer.

b) PYTHONSTARTUP: It contains the path of an initialization file containing Python source code. It is executed every time you start the interpreter. It is named as .pythonrc.py in Unix and it contains commands that load utilities or modify PYTHONPATH.
c) PYTHONCASEOK: It is used in Windows to instruct Python to find the first case-insensitive match in an import statement. Set this variable to any value to activate it.
d) PYTHONHOME: It is an alternative module search path. It is usually embedded in the PYTHONSTARTUP or PYTHONPATH directories to make switching module libraries easy.

5. Answer: [0].
   A new list object is created in the function and the reference is lost. This can be checked by comparing the ID of k before and after k = [1].
6. Answer: b. Variable names should not start with a number.