A program is read by computers $($Python interpreters$)$ and programmers, and

sometimes many programmers. It is important to write programs that are readable. A

readable program is easy to understand by a human.

It is a bad practice to use meaningless identifier like single character as variable name.

It is even worse to have too many identical identifiers as both global variable outside a

function definition and local variable inside a function definition, but they have

entirely different meaning.

A student has submitted a program using a lot of unclear variable identifiers. Please

help the teachers to understand this program.

$1$

$2$

$3$

$4$

$5$

$6$

$7$

$8$

$9$

$10$

$11$

$12$

$13$

$14$

$15$

$16$

$17$

$18$

$19$

$20$

$21$

$22$

a $=5$

b $=2$

c $=3$

s $=$ "message"

def a$($a$,$ b$,$ s$)$:

global c

for a in range $(3)$:

c $+=1$

s $=0$

return a $+$ b $+$ c $+$ s

s $=5$

def b$($a$,$ b$,$ s$)$:

c $=10$

return a $+$ b $+$ c $+$ s

print $($a$(1,2,3))$

print $($b$(1,2,3))$

print $($s$)$

$($i$)$ Is there any error when executing this program? If there is no error, write

down the output of the program

$($ii$)$ Study line $6.$ The identifier a is used as the name of a function. The same

identifier a is also used as a local parameter variable. Explain why it is not a

problem.

$($iii$)$ Study line $7.$ what is the purpose of putting global in front of the variable c$?$

What will be the difference in the situation of the variable c if the keyword

global is not exist like the situation in line $16?$