u3-script-data-structures

Question 1

What’s the difference between using + and append() with lists?

Answer 1

+ creates a new list (e.g., list1 + [5]), while append() modifies the existing list in-place (e.g., list1.append(5)). Example:

a = [1, 2, 3]
b = a + [4]  # b is new list
a.append(4)  # a is modified```

Question 2

Why can’t you modify elements in a tuple like you can in a list?

Answer 2

Tuples are immutable, meaning their elements cannot be changed after creation. To modify a tuple, you must create a new one. Example:

t = (1, 2, 3)
# t[0] = 0  # This fails
t = (0,) + t[1:]  # This works```

Question 3

What’s the difference between list assignment and list copying?

Answer 3

List assignment (b = a) creates a reference to the same list, while copying creates a new list. Changes to one affect/don’t affect the other respectively. Example:

a = [1, 2, 3]
b = a  # Changes to b affect a
c = a.copy()  # Changes to c don't affect a```

Question 4

How do you extract elements from a list using slicing?

Answer 4

Use the format list[start:stop:step]. Example:

a = list(range(100))
# Get every third element from index 50 to 69:
slice = a[50:70:3]```

Question 5

What’s the difference between sorted() and sort() in Python?

Answer 5

sorted() creates a new sorted list while sort() modifies the list in-place. Example:

list1 = [3,1,2]
list2 = sorted(list1)  # list1 unchanged
list1.sort()  # list1 is now sorted```

Question 6

How do you update multiple values in a dictionary at once?

Answer 6

Use the update() method to add or update multiple key-value pairs. Example:

d1 = {'a': 1, 'b': 2}
d2 = {'c': 3, 'd': 4}
d1.update(d2)  # d1 now has all pairs```

Question 7

How do you check if a string ends with a specific substring?

Answer 7

Use the endswith() method. Example:

filename = "image.png"
if filename.endswith(".png"):
    print("Is PNG file")```

Question 8

What’s the difference between the set operations “-“ and “&”?

Answer 8

- (difference) gives elements only in first set,
& (intersection) gives elements in both sets. Example:

set1 = {1,2,3}
set2 = {2,3,4}
only_in_set1 = set1 - set2  # {1}
in_both = set1 & set2  # {2,3}```

Question 9

How do you split a string and join it back together?

Answer 9

Use split() to divide string at delimiter,
join() to combine with new delimiter. Example:

text = "a,b	c"
parts = text.replace("	, ,").split(",")
new_text = ":".join(parts)```	

Question 10

What is a list comprehension and how is it used?

Answer 10

A concise way to create lists based on existing lists. Format: [expression for item in list if condition]. Example:

files = ["file1.png", "file2.txt"]
new_files = ["image" + f if f.endswith(".png") else "text" + f for f in files]```

Question 11

How do you merge two sorted lists while maintaining order?

Answer 11

Compare elements from both lists and add smaller one to result. Example:

merged = []
while i < len(list1) and j < len(list2):
    if list1[i] < list2[j]:
        merged.append(list1[i])
        i += 1
    else:
        merged.append(list2[j])
        j += 1```

Question 12

How do you work with nested data structures in Python?

Answer 12

Access elements using multiple indices/keys in sequence. Example:

nested = {"dept": {"e1": {"name": "Alice"}}}
name = nested["dept"]["e1"]["name"]```

Question 13

What’s the difference between extend() and append() for lists?

Answer 13

append() adds one element to the end, extend() adds all elements from an iterable. Example:

lst = [1, 2]
lst.append([3, 4])  # [1, 2, [3, 4]]
lst = [1, 2]
lst.extend([3, 4])  # [1, 2, 3, 4]```