013 String methods : Answers to exercises

Exercise 1

insert a new cell below here
what might a zero-length string look like? Try to generate one, and check its length.
the Hello there everyone example above has no spaces between the words. Copy the code and modify it to have spaces.
confirm that you get the expected increase in length.

# ANSWER

# insert a new cell below here
# what might a zero-length string look like? Try to generate one, and check its length.

t = ''
print (f'the length of {t} is {len(t)}')

# the `Hello there everyone` example above has no spaces between the words. Copy the code and modify it to have spaces.

space = ' '
s = "Hello" + space + "there" + space + "everyone"
print (f'the length of {s} is {len(s)}')

# confirm that you get the expected increase in length.
msg = '''
The old string had length 18
now, with two spaces, this has length 20 as expected
'''
print(msg)

the length of  is 0
the length of Hello there everyone is 20

The old string had length 18
now, with two spaces, this has length 20 as expected

Exercise 2

Insert a new cell below here
Take the multi-line string:

''' ----Remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance (typically from satellite or aircraft).---- '''

and use it to generate a single line string, without the - characters at either end.

# ANSWER

old_string = '''
----Remote sensing is the process of detecting and 
monitoring the physical characteristics of an 
area by measuring its reflected and emitted 
radiation at a distance (typically from 
satellite or aircraft).----
'''
print(old_string)

# replace newline with empty string!
# and strip the result after
new_string = old_string.replace('\n','').strip('-')
print(new_string)

----Remote sensing is the process of detecting and 
monitoring the physical characteristics of an 
area by measuring its reflected and emitted 
radiation at a distance (typically from 
satellite or aircraft).----

Remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance (typically from satellite or aircraft).

Exercise 3

Insert a new cell below here
Take the string

The Owl and the Pussy-cat went to sea In a beautiful pea-green boat, They took some honey, and plenty of money, Wrapped up in a five-pound note.

and split it into a list of sub-strings. * Then re-construct the string, separating each word by a colon character ':' * Print out the list of sub-strings and the re-constructed string

# Answer

# Take the string
string = '''
The Owl and the Pussy-cat went to sea 
In a beautiful pea-green boat, 
They took some honey, and plenty of money, 
Wrapped up in a five-pound note.
'''

# and split it into a list of sub-strings.
list_string = string.split()
# print this out
print(list_string)

# Then re-construct the string, separating each word by a colon character ':'
recon_string = ':'.join(list_string)
# print this out
print(recon_string)

['The', 'Owl', 'and', 'the', 'Pussy-cat', 'went', 'to', 'sea', 'In', 'a', 'beautiful', 'pea-green', 'boat,', 'They', 'took', 'some', 'honey,', 'and', 'plenty', 'of', 'money,', 'Wrapped', 'up', 'in', 'a', 'five-pound', 'note.']
The:Owl:and:the:Pussy-cat:went:to:sea:In:a:beautiful:pea-green:boat,:They:took:some:honey,:and:plenty:of:money,:Wrapped:up:in:a:five-pound:note.

# Answer
# the Hello there everyone example above has no spaces between the words. 
# copy the code and modify it to have spaces.

# generate a string called s
# and see how long it is

# lets have a spacer variable
spacer = ' '
quote = '"'
# add the spaces in
s = "Hello" + spacer + "there" + spacer + "everyone"
print ('the length of',quote+s+quote,'is',len(s))

# confirm that you get the expected increase in length.
# It is now 20 rather than 18 above

the length of "Hello there everyone" is 20

Exercise 4

Insert a new cell below here
copy the code above, and see what happens if you set i to be the value of length of the string.
why does it respond in this way?

# ANSWER

# copy the code
string = 'hello'

# length
slen = len(string)
print('length of', string, 'is', slen)

# copy the code above, and see what happens if you set `i` to be the value of length of the string. 
i = slen
print('character', i, 'of', string, 'is', string[i])

length of hello is 5



---------------------------------------------------------------------------

IndexError                                Traceback (most recent call last)

<ipython-input-18-c41bb38893d7> in <module>
     10 # copy the code above, and see what happens if you set `i` to be the value of length of the string.
     11 i = slen
---> 12 print('character', i, 'of', string, 'is', string[i])


IndexError: string index out of range

# ANSWER

# Why does it respond in this way?
msg = '''
 This fails with:

     IndexError: string index out of range

 because string[5] does not exist
 as the length of string is 5: we can
 only idex from 0 to 4
'''
print(msg)

 This fails with:

     IndexError: string index out of range

 because string[5] does not exist
 as the length of string is 5: we can
 only idex from 0 to 4

Exercise 5

The example above allows us to access an individual character(s) of the array.

Insert a new cell below here
based on the example above, print the string starting from the default start value, up to the default stop value, in steps of 2. This should be HloWrd.
write code to print out the 4\(^{th}\) letter (character) of the string s. This should be l.

# ANSWER

s = "Hello World"
print (s,len(s))

# based on the example above, print the string starting 
# from the default start value, up to the default stop value, in steps of `2`.

# default start -> None
start = None
# default stop -> None
stop  = None
skip  = 2
print (s[start:stop:skip])

# ANSWER

s = "Hello World"
# write code to print out the 4 𝑡ℎ  letter (character) of the string s.
# index 3 is the 4th character !!!
print(s[3])

Last update: November 11, 2022