Python core: check what you know

Already know some Python? Answer these 13 questions, about 7 minutes. Each topic you get fully right is marked Known on the Python roadmap, so you can skip it. Each one you miss is listed for you to study.

Don’t guess. Pick “I don’t know yet” when you’re not sure: a lucky guess would mark a topic Known that you still need to learn.

The 13 topics it checks

Classes: inheritance, MRO, super() and dunder methods
@property, class methods and static methods
Dataclasses
Iterators and generators
Closures
Decorators, with arguments and functools.wraps
Context managers
collections, itertools and functools
Type hints
is vs ==, shallow vs deep copy
Logging
pytest basics
pandas basics: DataFrames, filtering, groupby and merge

Question 1 of 13 · Predict the outputWhat does this print?

class A:
    def hi(self):
        return "A"
class B(A):
    def hi(self):
        return "B" + super().hi()
class C(A):
    def hi(self):
        return "C" + super().hi()
class D(B, C):
    pass
print(D().hi())

Question 2 of 13 · Multiple choiceCode all over the app writes item.price = x. You need to reject negative prices. What keeps every caller unchanged?
Add a set_price() method and ask everyone to use it.Make price a @property with a setter that checks the value.Make price a @staticmethod.Check the price in __repr__.I don’t know yet
Question 3 of 13 · Spot the bugWhy does Python refuse to create this class?
```
from dataclasses import dataclass

@dataclass
class Cart:
    owner: str
    items: list = []
```
owner needs a default value.Dataclasses can’t hold lists.A list default would be shared by every Cart; use field(default_factory=list).The decorator needs brackets.I don’t know yet
Question 4 of 13 · Predict the outputWhat does this print?
```
nums = (n * n for n in range(4))
print(sum(nums), sum(nums))
```
14 140 14An error14 0I don’t know yet
Question 5 of 13 · Predict the outputWhat does this print?
```
fns = []
for i in range(3):
    fns.append(lambda: i)
print([f() for f in fns])
```
[0, 1, 2][0, 0, 0][2, 2, 2]An errorI don’t know yet
Question 6 of 13 · Spot the bugAfter adding @timed, every decorated function returns None. Why?
```
def timed(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        func(*args, **kwargs)
        print(time.perf_counter() - start)
    return wrapper
```
wrapper calls func but never returns its result.functools.wraps hides the result.timed must return wrapper().*args can’t pass keyword arguments.I don’t know yet
Question 7 of 13 · Multiple choiceIn a @contextmanager function, where must the clean-up code go so it runs even when the with block raises?
Straight after yield.Before yield.In __init__.In a finally block around the yield.I don’t know yet
Question 8 of 13 · Multiple choiceYou need the 3 most common words in a list of a million words. What is shortest and fast?
sorted(set(words), key=words.count)[-3:]collections.Counter(words).most_common(3)itertools.groupby(words)max(words) three timesI don’t know yet
Question 9 of 13 · Predict the outputWhat happens when this runs?
```
def double(x: int) -> int:
    return x * 2

print(double("ab"))
```
It prints ababTypeError: x must be intIt prints 0A SyntaxErrorI don’t know yet
Question 10 of 13 · Predict the outputWhat does this print?
```
a = [[0], [0]]
b = a.copy()
b[0].append(1)
print(a, a == b, a is b)
```
[[0], [0]] False False[[0, 1], [0]] True True[[0, 1], [0]] True False[[0], [0]] True FalseI don’t know yet
Question 11 of 13 · Multiple choiceWhich line belongs in a library module?
logging.basicConfig(level=logging.DEBUG)print("paid", user)logging.info(f"paid {user}")log = logging.getLogger(__name__), then log.info("paid %s", user)I don’t know yet
Question 12 of 13 · Spot the bugThis test passes even when parse("") raises nothing. Why?
```
def test_empty():
    try:
        parse("")
        assert False, "should raise"
    except Exception:
        pass
```
assert False never runs.AssertionError is an Exception, so the except swallows the failure.Tests can’t use try.pass should be return.I don’t know yet
Question 13 of 13 · Multiple choiceA pandas report loops with iterrows over 3 million rows and takes 20 minutes. What is the fix for total amount per region?
df.groupby("region")["amount"].sum()Use apply instead of iterrows.Loop over regions and filter the table for each one.Convert the DataFrame to a list first.I don’t know yet

Answered 0 of 13.