Tuples, sets and dictionaries

Which one do I use?

Type	Looks like	Can change?	Duplicates?	Use it for
list	[1, 2, 3]	Yes	Allowed	An ordered collection
tuple	(1, 2, 3)	No	Allowed	Fixed data, like a coordinate
set	{1, 2, 3}	Yes	Removed	Unique items
dict	{"a": 1}	Yes	Keys are unique	Looking up by name

Tuples

tuples.py

point = (4, 7)
print(point[0])

x, y = point      # Unpacking
print(x, y)

try:
    point[0] = 9
except TypeError as error:
    print("Can't change a tuple:", error)

Output

4
4 7
Can't change a tuple: 'tuple' object does not support item assignment

Sets

sets.py

a = {1, 2, 3, 3, 3}
b = {3, 4}

print(len(a))           # Duplicates are gone
print(sorted(a | b))    # In either
print(sorted(a & b))    # In both
print(sorted(a - b))    # In a, not in b

Output

3
[1, 2, 3, 4]
[3]
[1, 2]

Dictionaries

dicts.py

student = {"name": "Riya", "age": 14, "marks": [78, 85]}

print(student["name"])
print(student.get("city", "Not given"))   # Safe if the key is missing

student["city"] = "Pune"                  # Add
student["age"] = 15                       # Change
del student["marks"]                      # Remove

for key, value in student.items():
    print(key, "->", value)

Output

Riya
Not given
name -> Riya
age -> 15
city -> Pune

word_count.py

# A classic: count words with a dictionary
text = "free money free prize free"
counts = {}
for word in text.split():
    counts[word] = counts.get(word, 0) + 1
print(counts)

Output

{'free': 3, 'money': 1, 'prize': 1}

Code challenge

Make a dictionary of 3 subjects and marks, then print the subject with the highest marks.

max(marks, key=marks.get) gives the key with the largest value.