strings, files and arrays

Question 1

mystring = “Hello”

how can i save the length of the string in the variable x

Answer 1

x = len(mystring)

Question 2

methods

Answer 2

-methods work similarly to functions.
- they are written like this

mystring.upper()

and return a value

Question 3

mystring = “Hello”

what methods will return
1) “HELLO”
2) “hello”

Answer 3

1) mystring.upper()
2) mystring.lower()

Question 4

mystring = “Hello”

what method will count the number of times “e” occurs in the string

Answer 4

mystring.count(“e”)

Question 5

mystring = “Hello”

what method will replace all instances of “e” with “x” in the string. (output “Hxllo”)

Answer 5

mystring.replace(“e”, “x”)

Question 6

mystring = “Hello”

how can i retreive the first letter of the string

Answer 6

mystring[0]

Question 7

mystring = “Hello”
write a loop which prints each letter of this string seperately.

Answer 7

for i in range (len(mystring)):
print(mystring[i])

Question 8

mystring = “Hello”

how can i take a “slice” of this string, leaving only the letters “ell”

Answer 8

mystring[1:3]

Question 9

mystring = “Hello”

how can i take a “slice” of this string, leaving out the first two letters

Answer 9

mystring[2:]

Question 10

mystring = “Hello”

how can i take a “slice” of this string, leaving out the last two letters

Answer 10

mystring[:3]

Question 11

what does slicing look like in psuedocode

Answer 11

mystring, substring(1,4)

Question 12

how to reference a file name in your program.

Answer 12

save the name as a string constant. eg.

FILENAME = “highscore.txt”

then it can be used as myfile

Question 13

given

FILENAME = “highscore.txt”
savetext= “200”

write some code to save 200 to the text document.

Answer 13

with open( FILENAME, “a”) as myfile:
myfile.write(savetext)

Question 14

given

FILENAME = “highscore.txt”

write some code to save the contents of the document to a variable x

Answer 14

with open (FILENAME, “r”) as myfile:
x= myfile.read()

Question 15

what are the conditions for reading a text file into a variable

Answer 15

• file must be text only
• must be in your python directory

Question 16

write a list called mylist , that holds the strings “a” “b” “c”

Answer 16

mylist = [“a” , “b”, “c”]

Question 17

what are items in a list called

Answer 17

elements
they can be different data types

Question 18

make an empty list called mylist. Then append “a” to the list.

Answer 18

mylist = []
mylist.append(“a”)

Question 19

given
mylist =[ “a”, “b”, “c”]
write one line of code to print “b” from the list

Answer 19

print(mylist[1])

Question 20

given
mylist =[ “a”, “b”, “c”]
write one line of code to ovverwrite the element “b” with “x”

Answer 20

mylist[1] = “x”

Question 21

mylist =[ “a”, “b”, “c”]

delete the element “b” using it’s element number

Answer 21

del mylist[1]

Question 22

mylist =[ “a”, “b”, “c”]

remove the element “b” using it’s content

Answer 22

mylist.remove(“b”)

Question 23

write a boolean expression that checks if the string “a” is in the list called mylist

Answer 23

“a” in mylist

Question 24

write an if structure that prints “correct” if the string “b” is found in the list mylist

Answer 24

if “b” in mylist:
print(“correct”)

Question 25

what is the difference between

1. mylist.sort()
2. sorted(mylist)

Answer 25

1. sort: a method that rearranges a list
2. sorted: a function that creates a new list and needs to be captured with a variable

Question 26

does slicing a list alter the value of the original list?

Answer 26

no

Question 26

list 6 operations that can be performed on data structures

Answer 26

appending
inserting
editing
deleting
traversing / searching
sorting

Question 26

what is a tuple

Answer 26

a python data structure
not mutable/ values cannot be changed
uses round brackets instead of square

Question 26

create a tuple called mytuple which holds the letters “a” “b” and “c”

Answer 26

mytuple = (“a”,”b”,”c”)

Question 26

what is a mutable data structure and give an example

Answer 26

a data structure that can change. Append, edit, reorganise etc.

eg. a list

Question 27

what operations can be done on a tuple

Answer 27

• traversing
• searching

Question 28

why would i use a tuple rather than a list

Answer 28

• store a list of data that dosen’t change, eg. months
• protect the program from unwanted errors

Question 29

mytuple = (“a”,”b”,”c”)

write a line of code to print the first element of this tuple.

Answer 29

print(mytuple[0])

Question 30

static vs dynamic data structures

Answer 30

static- fixed in size. eg. an array

dynamic - can get bigger and littler. eg. a list

Question 31

features of an array

Answer 31

fixed in size , can have empty spaces
all values must be the same data type
values remain at the same index address
values are shown in square brackets

Question 32

features of a list

Answer 32

mutable (can change size)
the index of a value can change as the list changes in size
values shown in square brackets

Question 33

traversing

Answer 33

visiting every value in a data structure.

eg. traverse a list/array/tuple with a for loop

Question 34

2D array

Answer 34

• can be thought of as a table of rows and columns
• each position is identified by row value and column value

myarray[4,2]

Question 35

2D list

Answer 35

a list of lists
every element is identified by two numbers

mylist[2][4]