ITI1120-Lab 4 Order of Execution, Strings, For Loops and Range Function Solved

In       Python  interpreter  assign   string            ‘good’    to    variable   s1,  ‘bad’      to    variable ‘s2’ and   ‘silly’      to    variable s3.  Write   Python  expressions involving   strings   s1,  s2,  and s3 that   correspond  to:

a)        'll' appears in     s3

b)       the       blank       space      does    not  appear    in     s1

c)        the       concatenation       of     s1,    s2,   and s3

d)       the       blank       space      appears  in    the  concatenation       of     s1,    s2,   and s3

e)        the       concatenation       of     10    copies     of     s3

f)          the       total        number  of    characters      in     the    concatenation       of     s1,   s2,    and s3

Introduction to Computing Using Python by Lj. Perkovic 

Indexing  operator, revisited
The indexing operator s[i:j] :      the slice       of    s starting   at    index      i and   returns the character ending before   index     j

at index i (as a s[i:] :    the slice      of    s starting   at    index     i single character 

string).                           s[:j] :                                                                                the                                                                               slice                                                                                   of                                                                                    s ending                                                                          before                                                                            index                                                                                    j

                                                                 -5           -4            -3            -2            -1

çNote: There are no blank  for visibility purposes

Introduction to Computing Using Python by Lj. Perkovic

Task 2
Start python interpreter

1.    In python interpreter, create aha variable and assign ‘abcdefgh’ to it.

2.    Then write Python expressions (in the interpreter) using string aha and the indexing operator that evaluate to:

a)‘abcd’

b)‘def’

c)‘h’

d)‘fg’

e)‘defgh’

f)‘fgh’

g)‘adg’

h)‘be’

Introduction to Computing Usi

String   methods
Usage
Explanation
s.capitalize()
returns   a      copy        of     s with         first character       capitalized
s.count(target)
returns   the  number  of     occurences         of     target in   s
s.find(target)
returns   the  index       of     the  first         occurrence    of     target in   s
s.lower()
returns   lowercase      copy        of     s
s.replace(old, new)
returns   copy        of     s with   every         occurrence    of     old replaced         with new
s.split(sep)
returns   list   of     substrings      of     s,         delimited        by    sep
s.strip()
returns   copy        of     s without         leading   and trailing   whitespace
s.upper()
returns   lowercase      copy        of     s 
Strings    are immutable; none      of    the  string    methods      modify  string    s

Introduction to Computing Using Python by Lj. Perkovic Task 3

Copy/paste the following expression (in black) to Python Interpreter:

s = '''It was the best of times, it was the worst of times; it was the age of wisdom, it was the age of foolishness; it was the epoch of belief, it was the epoch of incredulity; it was ...'''

(The beginning of A Tale of Two Cities by Charles Dickens.) 

Then do the following, in order:

(a) Write a sequence of statements that produce a copy of s, named newS, in which characters ., ,, ;, and \n have been replaced by blank spaces. (b) Remove leading and trailing blank spaces in newS (and name the new string newS). 

(c)   Make all the characters in newS lowercase (and name the new string newS). 

(d)   Compute the number of occurrences in newS of string 'it was'. 

(e)   Change every occurrence of was to is (and name the new string newS).

Task 4 
a)             Follow   the  link in    (b)   and trace       through the  two Python   Vizualizer       examples              that have       “Code       Lence     1” and    “Code    Lence     2” in       the  caption. You do   that by   clicking       Forward until       the  program ends,       like  we  did  it     class       (It    does       not  matter   here       that it     says       Python   2.7. For  these      two programs       Python   2     and 3     behave          the       same).    

b)            Then      Answer  the  two multiple choice       questions      at    the  end

https://runestone.academy/runestone/static/thinkcspy/Functions/Functionsthatreturnvalues.html

c)             Then      follow    this link and         do   the       two multiple choice exercises:https://runestone.academy/runestone/static/thinkcspy/Functions/FlowofExecutionSummary.html

Task    5: More    tracing  and   print vs return

Open     the program       called    print-vs-return-and-function-calls.py,       provided      in    this lab.

The lines       the start       with       #     are       commented out. Thus      Python  will       ignore   them.    In    other     words,       if     you press     Run Module the       lines       that        start       with       # will not be   executed.     Uncomment       the lines       as    instructed    in    the       file. Each      time       you do,  save       and press     “Run      Module”.     But       before   you press     “Run       Module”,     write     down     what       you think      the program       will       print.     Then      press     “Run       Module”      and compare.     

Note:    once              you uncomment a       line as    instructed,   leave     it     as       is     (do not put back       the       comments,  but rather    continue       with       the next       set  of    lines       you are  instructed    to       uncomment).

Programming   exercise:   Solved   Problem    
Suppose   that           you     are given      the following  two     problems      to  solve.  Read   the two      problems. Think  about  how      you     would solve   them,  and      then    open   and     study  the      two     provided  solutions  in      prog_solved_v1.py   and      prog_solved_v2.py.        Run      both.

Version    1:   Write  a    program      that     asks     a    user    for her      name  and     age      and      prints  a    nice     message      stating if    the user    is   eligible      to  vote.

Version    2: Write    a    program that    asks     a    user    for name      and     age      and     prints  a      nice     message   stating if    the      user    is   eligible      to  vote.      As  a    part     of  your    solution      the program   should have    a      function   called  is_eligible that      given   the age      as  input      parameter      returns     true      or  false    depending     on      weather   the age      is   less      than    18  or  not.     

Programming  exercise  1 
Repeat    the  exercise  in     the  previous question (version  2),    where     in     addition you  need        to ask  the  user for   their        citizenship     and if they are  currently in     prison     convicted       for   a criminal  offence.  Your        program should    print a      nice message telling     the  user if      they are eligible   to     vote (i.e. if      they are  18+, Canadian and do    not  live  in     prison     convicted       for   a criminal  offence,  then        they can  vote. Otherwise      not).        You should    modify function is_eligible       so    it      takes       to additional      paramters      as    input.      In particular       the  head        of     the  function should be:           is_eligible(age,      citizenship,    prison)

Your        program should    work       if      the  user enters     any  of     the  following        versions of answers for   the  two new questions:

Canadian 

Canada 

Canada canadian 

Yes

YES

No no and so on

Note that  in       Canada,     one   can   vote  even if        in          prison        convicted  for    a        criminal     offence.          This            example    if        fictional.

Programming  exercise  2 
Write    a     function      called   mess     that       takes    a     phrase  (i.e.,      a     string)  as       input    and then     returns the copy     of       that      phrase  where  each     character       that      is    one of   the last       8       consonants of   English alphabet     is       capitalized  (so,       r,    s,    t,    v,    w,       x,y ,       z)    and where  each     blank       space    is    replaced     by   dash.

For this question,    use a     for  loop      over       characters  of   a     string,  and       “accumulator”. (We      will see,      or       have     seen,    that      in   Lecture 8       on  Monday).   When   called   from       the python shell,    your      function       should  behave as   follows:

mess('Random access memory  ') 

'Random-acceSS-memoRY--'

mess('central processing   unit.')

‘cenTRal-pRoceSSing---uniT.'

 

Built-in function range()
Function range() is used to iterate over a sequence of numbers in a specified range

•       This iterates over the n numbers 0, 1, 2, …, n-1 for i in range(n):

•       This iterates over the n numbers k, k+1, k+2, …, n-1 for i in range(k, n):

•       This iterates over the n numbers k, k+c, k+2c, k+3c, …, n-1 for i in range(k, n, c):

In particular the first time a program encounters a forloop it creates the variable whose name follows the keyword for. In the above examples, the variable name is  i. Then that variable, i in this case, takes values in the given range one by one. Each time it takes the next value it enters the for-loop and executes its body. The for-loop terminates after i has taken on all the values in the range, as shown above) 

 

 

Python   Visualizer   
Go  to    Python  Visualizer     here       (make sure       you choose  Python  3) http://www.pythontutor.com/visualize.html#mode=edit

 
 for i in range(1,10, 3):

print(i)
 and copy/paste, only       by   one,       the following      loops     to    it     and click Forward       to    visualize       the execution. Pay attention      what      is     assigned       to variable i and      when     does      loop terminate.

 Task 6
Before attempting the following exercise study the examples from the previous slide. 

Then open a new file in IDLE and write a program with 6 separate for loops that will print the 6 sequences listed below in parts a) to f). (you do not have to print commas, but you can if you know how to). 

Note that if you put ,end=" ” at the end of a print function call, then the print function will print the blank space when it finishes rather than go to the new line.

Eg: this prints numbers 0 to 9 in one line 

for i in range(10): print(i,end=" ")

0 1 2 3 4 5 6 7 8 9

a)0, 1, 2, 3, 4, 5, 6, 7, 8 , 9, 10

b)1, 2, 3, 4, 5, 6, 7, 8, 9

c)0, 2, 4, 6, 8

d)1, 3, 5, 7, 9

e)20, 30, 40, 50, 60

f)10, 9, 8, 7, 6, 5, 4, 3, 2, 1

Programming  exercise 3: 

Open     the file  ex23n8.py.   Inside    of    that file:

1.             write     a     function       called       print_all_23n8(num),      that        takes       as    input     a     non-negative       integer  num and      prints    all   the       the non-negative      numbers       smaller  than       num that      are       divisible by   2     or    3     but not 8.       You should   use the function       that       is     already  present in    the file  (and       that        you developed   for  the last       lab)

2.             Outside of    that        function       ask  the       user       for  a     non-negative       integer. Your      program       should       then       print      all   non-negative       numbers      that        are  divisible by   2       or    3     but not 8,    by   making  a       call  to    function       print_all_23n8

3.             Run       your       program       and test it       by   entering,      for  example,             1000      when     prompted    for  a       number

Programming exercise 4:   

This program: for i in range(4): print("*************")

Prints         :

*************

*************

*************

*************

Write         a        program    that  asks  a        user  for    a         positive     integer       and   a        character. And  then         draws         half   piramid      with  the    given          number         of                raws using          that  character. For         example    if                  the    user  enter          3        and   $,         your program    should       draw (that is,      print):

$                                       #         

$$

###        $$$

#####       

Bonus                                                                                                 excercise:                                                                                             #######      

For   a        callenge,   draw a        real   pirmaid      like    the         one   to      the    right #########     that         should       be     displayed  if        the    user  entered     10         and   #        ###########    

#############   

###############  

################# 

19

###################

Programming  exercise 5: 

1.             Write    a     program       that        asks       a       user       for  a     positive integer  and       then       prints    all   the divisors of       the given     integer. For example       if       the user       entered 6,    the program       should   print:     1,    2,    3,    6     

2.             Add       a     function,      called    prime, to       this program.      Function       prime takes     a     positive integer  as    input       parameter   and tests      if     it     is     a       prime    (that      is,    it     returns  true       if     the given     number is     a     prime       and false       otherwise).  Recall    that       a     number is     prime    if     it     at       least      2     and if     it     is     only       divisible by   1     and itself.     Then       make     a     call  to    this function       and print      the message       stating   if       the number the user       inputted       in       1)    is     a     prime.

3.             Copy/paste your       whole    solution into       Python  Visualizer,    click       through       with       Forward       to    understand       see how       it     runs

4.             Bonus   exercise:      Write     a     program       that        asks       a     user       for  a       positive integer, n,            and prints       all   the primes  smaller  than       n.

Making  a   table 
With   these  tools,  you     now can      make  a    program  that prints nice    tables.      See here:

http://interactivepython.org/courselib/static/thinkcspy/MoreAboutIteration/SimpleTables.html