---
# System prepended metadata

title: Python Self-Check 4
tags: [Python]

---

---
tags: Python
---
# Python Self-Check 4
CS 1358 Introduction to Programming in Python
Fall Semester 2022
Prof. Pai H. Chou

Self-Check 1
Due Date: --

Answer the following questions to check your understanding of your material. Expect the
same kind of questions to show up on your tests. For this course, we use vi and vim
interchangeably.

## 1. Definitions and Short Answers
1. Given the command shown on the lecture slide
```
$ uniq mary.txt
What is
the prompt? $
the program name? uniq
the command-line argument? mary.txt
```
2. What does the uniq program do?
```
filters out repeated lines in a file
```
3. What does the cat program do?
```
concatenate and print files
```
4. What does the grep program do?
```
print matched lines in the input file(s)
```
5. Is it possible that uniq and cat produce the same output?  How?
```
Yes.It is possible.
When every lines in file has the same pattern
```
6. Given the command shown on the lecture slide
```
$ grep class myfile.py
```
What is the purpose of
```
class 
myfile.py
```
```
class is the pattern we want to find in file
myfile.py is file name
```
7. Given the command
```
$ cat *.py
```
What is the meaning of *.py?
```
to concatenate and print every .py files in the working directory 
```
8. What does the following command do?
```
$ python3 prog.py
```
```
python interpreter interprets the prog.py file
```
9. What is a shbang in a Python program?  Where is it placed inside a Python program?
```
shbang line tells the shell which interpreter to use
shbang is comment to Python
```
10. What does the command do:
```
$ chmod +x prog.py
```
```
add the executable permission to prog
```
11. What is the value of 
```
len([3, 7, 2, 0, 8])                //5
len(['hello', 'world', 'goodbye'])  //3
len('admin')                        //5
```
12. Suppose you run the command
```
$ python3 showargs.py  hello  world  goodbye
Inside the showargs.py program, suppose you have
import sys
What is the value of sys.argv?        //['showargs.py', 'hello', 'world', 'goodbye']
What is the value of len(sys.argv)?   //4
What is the value of sys.argv[1:]?    //['hello','world','goodbye']
```
13. If the command $ python3 showargs.py hello world is used to run the Python program, what is printed by the statement
```
import sys
sys.stderr.write('cannot open input file %s\n' % sys.argv[1])
?
```
```
cannot open input file hello
```
14. If the file mary.txt contains the following lines
```
Mary had a little lamb
little lamb, little lamb
Mary had a little lamb
its fleece was white as snow
?
```
what is the value of L after executing the following statements?
```
fh = open('mary.txt', 'r')
L = fh.readlines()
fh.close()
```
```
['Mary had a little lamb\n','little lamb, little lamb\n','Mary had a little lamb\n','its fleece was white as snow\n']
```
15. What is the purpose of end='' in the statement ?
```
print(line, end='')
```
```
print the value of line without newline
```
16. Explain why
'hello'.find('e')
results in the integer value of 1, while 
'hello'.find('a')
results in -1.
```
if find function return value >= 0 then found a match.
< 0 means no match.
```
17. Rewrite the string literal "hello, I'm John." using
```
single quotes                 //'hello, I\'m John.'
triple single quotes          //'''hello, I'm John.'''
triple double quotes          //"""hello, I'm John."""
```
18. Rewrite the string literal 'she says, "This is great!" and left' using
```
double quotes                //"she says, \"This is great!\" and left"
triple single quotes         //'''she says, "This is great!" and left'''
triple double quotes         //"""she says, "This is great!" and left"""
```
19. Rewrite the string literal '\\n means newline' using a raw string.
```
r'\n means newline'
```
20. After executing the statement
t = 'hello' "world"
What is the value of t?
```
helloworld
```
21. What is the value of
```
len("hello")           //5
len("I\tam\there")     //9
len('McDonald\'s')     //10
```
22. Rewrite the following triple-quoted string literal using a non-triple-quoted string literal
```
sourceCode = '''<html>
<body>Welcome</body>
<html>'''
on one single line      //sourceCode = '<html>\n<body>Welcome</body>\n<html>'
on three separate lines 
//sourceCode = '<html>\n'\
'<body>Welcome</body>\n'\
'<html>\n'
```
23. Assume 
month = 7
day = 4
year = 2019
How do you format the date using % formatting so that it appears as strings (expressed as string literals)
```
'7/4/2019'            //'%d/%d/%d' % (month ,day, year)
'07/04/2019'          //'%02d/%02d/%d' % (month ,day, year)
```
24. What is the value of
```
'%9.2f' % 13.5                //'     13.50'
'%9.2f' % 123456789.0193      //'123456789.01'
```
25. What is the meaning of 5e2?  What is its data type?
```
500
float
```
26. What is the value of 5e-2?
```
0.05
```
27. What is the value of '%c' % 100, given that ord('a') has the value of 97?
```
'd'
```
28. What is the format string S such that S.format(month, day, year)
is equivalent to the traditional formatting of
```
 '%d/%d/%d' % (month, day, year) 
```
```
f'{month}/{day}/{year}'
'{0}/{1}/{2}'.format(month, day, year)// string format
```
29. What is the value of the expression
```
'one {0}, two {0}s, three {0}s'.format('apple')
```
```
'one apple, two apples, three apples'
```
30. What is the format string S such that 
S.format(12)
evaluates to the string
'12 decimal is 0c hex and 14 octal'
```
'{0} decimal is {0:02x} hex and {0:o} octal'
```
31. What is the value of the expression
```
'lastname {1}, firstname {0}'.format('John', 'Smith')
```
```
'lastname Smith, firstname John'
```
32. Rewrite the following expressions as f-string:
```
'%d/%d/%d' % (month, day, year)
'{:02d}/{:02d}/{:04d}'.format(month, day, year)
```
```
f'{month}/{day}/{year}'
f'{month:02d}/{day:02d}/{year:04d}'
```
33. What is the value of the expression
```
'www.nthu.edu.tw'.split('.')
'Mary had a\nlittle lamb'.split()
```
```
['www', 'nthu', 'edu', 'tw']
['Mary', 'had', 'a', 'little', 'lamb']
```
34. Suppose you type the unix command wc (lightblue) and get the output (lightgreen) as shown below:
```
$ wc mult.py//lightblue
       9      32     249  mult.py//lightgreen
```
What are the meanings of 9, 32, and 249?
```
9 lines 32 words 249 characters
```
35. What is the value of the expression
```
'(' + ')('.join(['a', 'b', 'c', 'd']) + ')'
''.join('Mary had a little lamb'.split())'
```
```
'(a)(b)(c)(d)'
'Maryhadalittlelamb'
```
36. Assume you have 
import string
What is the value of
```
string.punctuation            //!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
string.digits                 //0123456789
string.ascii_lowercase        //abcdefghijklmnopqrstuvwxyz
string.whitespace             
//


(characters space, tab, linefeed, return, formfeed, and vertical tab.)
string.printable              
//0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~



```
## 2. Programming
1. Write a program that prompts the user to input two strings and reports the two strings' lengths, by reporting the shorter string first. But if they are of the same length then keep them in the original order.  For example, (blue text = typed input, green highlight = program printout)
$ python3 compstr.py
Enter a string: Great
Enter another string: job
Shorter string: job (length 3)
Longer string: Great (length 5)
$ python3 compstr.py
Enter a string: Mary
Enter another string: lamb
First string: Mary (length 4)
Second string: lamb (length 4)
$ 
Note that in case the strings are of different lengths, the program says Shorter and Longer, but in case the strings are of equal length, the program says First and Second.  You don't actually print in color… the letters are colored for illustration purpose only.
2. Write a Python program named catn.py by modifying the template code to implement the unix utility command cat with -n option, which adds the line number in front of every line of a file.
    a. First version: support the command with optional -n flag and one file.  Note that the line number is formatted 
    ```
    $ python3 catn.py mary.txt
    Mary had a little lamb
    little lamb, little lamb
    Mary had a little lamb
    its fleece was white as snow
    $ python3 catn.py -n mary.txt
     1  Mary had a little lamb
     2  little lamb, little lamb
     3  Mary had a little lamb
     4  its fleece was white as snow
    $ 
    ```
    b. econd version: handles one or more files with optional -n flag.  In case of multiple files, the line number restarts from 1.
