Strings, String and List Methods, Exceptions

Question 1

What is the most widely used code to turn characters into numbers?

Answer 1

ASCII short for American Standard Code for Information Interchange

Question 2

What does I18N stand for?

Answer 2

Internationalisation

Question 3

What is a code point?

Answer 3

A code point is a number which makes a character. For example, 32 is a code point which makes a space in ASCII encoding. We can say that standard ASCII code consists of 128 code points.

Question 4

What is a code page?

Answer 4

A code page is a standard for using the upper 128 code points to store specific national characters. For example, there are different code pages for Western Europe and Eastern Europe, Cyrillic and Greek alphabets, Arabic and Hebrew languages, and so on.

Question 5

What does unicode do?

Answer 5

Unicode assigns unique (unambiguous) characters (letters, hyphens, ideograms, etc.) to more than a million code points.

The first 128 Unicode code points are identical to ASCII, and the first 256 Unicode code points are identical to the ISO/IEC 8859-1 code page (a code page designed for western European languages).

Question 6

What does UCS-4 do?

Answer 6

UCS-4.

The name comes from Universal Character Set.

UCS-4 uses 32 bits (four bytes) to store each character, and the code is just the Unicode code points’ unique number. A file containing UCS-4 encoded text may start with a BOM (byte order mark), an unprintable combination of bits announcing the nature of the file’s contents. Some utilities may require it.

Question 7

Are strings mutable or immutable?

Answer 7

immutable

Question 8

i_am = ‘I\‘m’
print(len(i_am))

What is the output?

Answer 8

3
i ‘ m

Question 9

multiline = ‘Line #1
Line #2’

print(len(multiline))

What is the ouput?

Answer 9

Syntax Error

string cannot be on more than 1 line in ‘’ need to use ‘’’ ‘’’ or “”” “””

Question 10

multiline = “"”Line #1
Line #2”””

print(len(multiline))

what is the output?

Answer 10

15

as there is a white space \n between the two lines that need to be counted

Question 11

What are the two operations you can perform on strings?

Answer 11

concatenation +
replication *

Question 12

What is overloading?

Answer 12

The ability to use the same operator against completely different kinds of data

Question 13

What does ord do and what is its requirement?

Answer 13

ord() (ordinal) turns character in ASCII code point value

The function needs a one-character string as its argument - breaching this requirement causes a TypeError exception, and returns a number representing the argument’s code point.

Question 14

What does char() do?

Answer 14

code point number –> corresponding character

Question 15

ORD() NEEDS A STRING !!!!!!!!!!!
CHR() NEEDS A INT !!!!!!!!!!!!!!!

Question 16

Strings are sequences therefore you can ….

Answer 16

iterate through them and index them

Question 17

What is slicing?

Answer 17

taking a part of a string

e.g. x = kate
x[2:4]
–> te

Question 18

alphabet = “abcdefghijklmnopqrstuvwxyz”

print(“f” in alphabet)

what is the output?

Answer 18

True

can also use not in

Question 19

What three things can you not do with a string that you can with a list?

Answer 19

del (a specific element)
insert
append

Question 20

alphabet = “bcdefghijklmnopqrstuvwxy”

alphabet = “a” + alphabet

What is the output?

Answer 20

“abcdefghijklmnopqrstuvwxy”

Question 21

t = ‘The Knights Who Say “Ni!”’
min(t)

Answer 21

the space ‘ ‘

Question 22

What will cause an error using the min()?

Answer 22

if the string or list is empty

Value Error

Question 23

print(min(“aAbByYzZ”))

Answer 23

A

comes first in ASCII

Question 24

print(max(“aAbByYzZ”))

Answer 24

z

Question 25

print("aAbByYzZaA".index("b"))

Answer 25

2 Note: the element searched for must occur in the sequence - its absence will cause a ValueError exception.

Question 26

What does the index method do?

Answer 26

The index() method (it's a method, not a function) searches the sequence from the beginning, in order to find the first element of the value specified in its argument. The method returns the index of the first occurrence of the argument (which means that the lowest possible result is 0, while the highest is the length of argument decremented by 1).

Question 27

What does the list function do?

Answer 27

The list() function takes its argument (a string) and creates a new list containing all the string's characters, one per list element. print(list("abcabc")) -->['a', 'b', 'c', 'a', 'b', 'c']

Question 28

What does the count method do?

Answer 28

The count() method counts all occurrences of the element inside the sequence. The absence of such elements doesn't cause any problems.

Question 29

for ch in "abc": print(chr(ord(ch) + 1), end='') What is the output?

Answer 29

bcd

Question 30

What does the capitalize() method do?

Answer 30

if the first character inside the string is a letter (note: the first character is an element with an index equal to 0, not just the first visible character), it will be converted to upper-case; all remaining letters from the string will be converted to lower-case.

Question 31

print(' Alpha'.capitalize())

Answer 31

' alpha'

Question 32

What does center() do?

Answer 32

The one-parameter variant of the center() method makes a copy of the original string, trying to center it inside a field of a specified width. The centering is actually done by adding some spaces before and after the string The two-parameter variant of center() makes use of the character from the second argument, instead of a space.

Question 33

print('[' + 'gamma'.center(20, '*') + ']')

Answer 33

[*******gamma********] (brainscape messed up should be 20 characters over all)

Question 34

What does the endswith() method do?

Answer 34

checks if the given string ends with the specified argument and returns True or False, depending on the check result. if "epsilon".endswith("on"): print("yes") else: print("no") yes

Question 35

What does the find() method do?

Answer 35

The find() method is similar to index(), which you already know - it looks for a substring and returns the index of first occurrence of this substring, but: it's safer - it doesn't generate an error for an argument containing a non-existent substring (it returns -1 then) it works with strings only - don't try to apply it to any other sequence. print("Eta".find("ta")) --> 1 print("Eta".find("mma")) --> -1

Question 36

What does two parameter find() do?

Answer 36

if you want to perform the find, not from the string's beginning, but from any position, you can use a two-parameter variant of the find() method. Look at the example: print('kappa'.find('a', 2)) ---> 4 There is also a three-parameter mutation of the find() method - the third argument points to the first index which won't be taken into consideration during the search (it's actually the upper limit of the search). print('kappa'.find('a', 2, 4)) --------> -1

Question 37

What does isalnum() do ?

Answer 37

The parameterless method named isalnum() checks if the string contains only digits or alphabetical characters (letters), and returns True or False according to the result. spaces are not a digit or a char

Question 38

What does isalpha() do?

Answer 38

checks if the string only contains letters

Question 39

What does isdigit() do?

Answer 39

checks if string only contains digits

Question 40

What does islower() so?

Answer 40

returns true is all characters are lower case

Question 41

What does isspace() do?

Answer 41

The isspace() method identifies whitespaces only - it disregards any other character (the result is False then).

Question 42

What does isupper() do?

Answer 42

returns true is all characters are upper case

Question 43

What does the join() method do?

Answer 43

the method performs a join - it expects one argument as a list; it must be assured that all the list's elements are strings - the method will raise a TypeError exception otherwise; all the list's elements will be joined into one string but... ...the string from which the method has been invoked is used as a separator, put among the strings; print(",".join(["omicron", "pi", "rho"])) --> omicron,pi,rho

Question 44

What does lower() do?

Answer 44

The lower() method makes a copy of a source string, replaces all upper-case letters with their lower-case counterparts, and returns the string as the result. Again, the source string remains untouched.

Question 45

What does the lstrip() method do?

Answer 45

The parameterless lstrip() method returns a newly created string formed from the original one by removing all leading whitespaces.

Question 46

print("www.cisco.com".lstrip("w."))

Answer 46

cisco.com print("www.wwwww...w....cisco.com".lstrip("w.")) ---> cisco.com

Question 47

What does the replace() method do?

Answer 47

The two-parameter replace() method returns a copy of the original string in which all occurrences of the first argument have been replaced by the second argument.

Question 48

What does the third parameter in replace() do?

Answer 48

Limits the number of replacements print("This is it!".replace("is", "are", 1))-----thare is it! print("This is it!".replace("is", "are", 2))---thare are it!

Question 49

What does rfind() method do?

Answer 49

Same as find() but starts search from the end of the string can have three parameters what to search for , start, finish

Question 50

What does rstrip() do?

Answer 50

same as lstrip() but starts from end of string print("cisco.com".rstrip(".com")) -------> cis

Question 51

What does split() do?

Answer 51

The split() method does what it says - it splits the string and builds a list of all detected substrings. The method assumes that the substrings are delimited by whitespaces - the spaces don't take part in the operation, and aren't copied into the resulting list.

Question 52

What does startswith() do?

Answer 52

The startswith() method is a mirror reflection of endswith() - it checks if a given string starts with the specified substring.

Question 53

What does strip() do?

Answer 53

The strip() method combines the effects caused by rstrip() and lstrip() - it makes a new string lacking all the leading and trailing whitespaces.

Question 54

What does swapcase() do?

Answer 54

The swapcase() method makes a new string by swapping the case of all letters within the source string: lower-case characters become upper-case, and vice versa.

Question 55

What does title() do?

Answer 55

The title() method performs a somewhat similar function - it changes every word's first letter to upper-case, turning all other ones to lower-case.

Question 56

What does upper() do?

Answer 56

Last but not least, the upper() method makes a copy of the source string, replaces all lower-case letters with their upper-case counterparts, and returns the string as the result.

Question 57

How does python compare strings?

Answer 57

It compares them using the normal comparisons e.g. ==, !=, >, >=, <, <= using the character ASCII code therefore 'A' < 'a'

Question 58

Output of '80' > '20'

Answer 58

True but remember they are strings so the comparison is the ASCII code point

Question 59

What are the only two comparison you can perform against ints and strings? e.g. 10 ....... '10'

Answer 59

== and != > and < will give a type error

Question 60

Whats the difference between sort() and sorted()?

Answer 60

sort() is a method which affects the list itself, no new list is created. Ordering is performed in situ by the method. sorted() is a function. The function takes one argument and returns a new list.

Question 61

How do you convert a number (int or float) to a string?

Answer 61

str(number)

Question 62

How do you convert a string to a number (int or float)?

Answer 62

Only works if the string is a valid number. will get a value error if not. int(num) float(num)

Question 63

True or False '11' < '8'?

Answer 63

True as '11' is just two 1s which come before 8 and therefore have lower ASCII number

Question 64

s1 = 'Where are the snows of yesteryear?' s2 = s1.split() s3 = sorted(s2) print(s3[1])

Answer 64

are because Where has a capital and therefore comes first in ASCII values

Question 65

try: print("1") x = 1 / 0 print("2") except: print("Oh dear, something went wrong...") print("3")

Answer 65

1 Oh dear, something went wrong... 3

Question 66

What order are except branches searched in?

Answer 66

The same order they appear in the code

Question 67

try: print("Let's try to do this") print("#"[2]) print("We succeeded!") except: print("We failed") print("We're done")

Answer 67

Let's try to do this We failed We're done (index error in line 3)

Question 68

How would you handle two or more exceptions in the same way?

Answer 68

try: : except (exc1, exc2): :

Question 69

What does raise exc do?

Answer 69

The raise instruction raises the specified exception named exc as if it was raised in a normal (natural) way: raise exc The instruction enables you to: simulate raising actual exceptions (e.g., to test your handling strategy) partially handle an exception and make another part of the code responsible for completing the handling (separation of concerns).

Question 70

Where can 'raise' be used on its own?

Answer 70

Inside the expect branch

Question 71

What does assert expression do?

Answer 71

evaluates the expression and raises the AssertError exception when the expression is equal to zero, an empty string, or None. You can use it to protect some critical parts of your code from devastating data.

Question 72

Describe Arithmetic Error?

Answer 72

Location: BaseException ← Exception ← ArithmeticError Description: an abstract exception including all exceptions caused by arithmetic operations like zero division or an argument's invalid domain

Question 73

Describe Assertion Error

Answer 73

Location: BaseException ← Exception ← AssertionError Description: a concrete exception raised by the assert instruction when its argument evaluates to False, None, 0, or an empty string

Question 74

Describe Base Exception

Answer 74

Location: BaseException Description: the most general (abstract) of all Python exceptions - all other exceptions are included in this one; it can be said that the following two except branches are equivalent: except: and except BaseException:.

Question 75

Describe Index Error

Answer 75

Location: BaseException ← Exception ← LookupError ← IndexError Description: a concrete exception raised when you try to access a non-existent sequence's element (e.g., a list's element)

Question 76

Describe Keyboard Interrupt

Answer 76

Location: BaseException ← KeyboardInterrupt Description: a concrete exception raised when the user uses a keyboard shortcut designed to terminate a program's execution (Ctrl-C in most OSs); if handling this exception doesn't lead to program termination, the program continues its execution. Note: this exception is not derived from the Exception class. Run the program in IDLE.

Question 77

Describe Lookup Error

Answer 77

BaseException ← Exception ← LookupError Description: an abstract exception including all exceptions caused by errors resulting from invalid references to different collections (lists, dictionaries, tuples, etc.)

Question 78

Describe Memory Error

Answer 78

Location: BaseException ← Exception ← MemoryError Description: a concrete exception raised when an operation cannot be completed due to a lack of free memory.

Question 79

Describe Overflow Error

Answer 79

Location: BaseException ← Exception ← ArithmeticError ← OverflowError Description: a concrete exception raised when an operation produces a number too big to be successfully stored

Question 80

Describe Import Error

Answer 80

Location: BaseException ← Exception ← StandardError ← ImportError Description: a concrete exception raised when an import operation fails

Question 81

Describe Key Error

Answer 81

Location: BaseException ← Exception ← LookupError ← KeyError Description: a concrete exception raised when you try to access a collection's non-existent element (e.g., a dictionary's element)

Question 82

print(ord('c') - ord('a'))

Answer 82

2