Python for Beginners — Proficiency Exam

15 questions · pass with 50%

1. Why create a virtual environment instead of installing every package globally?
Python cannot run files without a venv folder named globalpip only works inside GitHubEach project can have its own package versions without breaking other projectsVirtual environments replace the need to save .py files
2. What does python -m pip install some-package do that typing pip install can fail to do?
It uses the same Python interpreter you invoked, so the package lands in that environmentIt compiles the package into a phone appIt skips PyPI and invents the packageIt always installs Python 2
3. You cloned a project that includes requirements.txt but not a .venv folder. What should you do?
Copy someone else's .venv directory from another computerCreate a new venv, activate it, then pip install -r requirements.txtDelete requirements.txt so pip can guessInstall packages globally and ignore the file
4. The user types 21 at an input() prompt. What type is the value you receive?
int 21, because it looks like a numberstr '21', until you convert itfloat 21.0 automaticallybool True because the input succeeded
5. a = [1, 2]; b = a; b.append(3). What is a?
[1, 2] because assignment copies lists[1, 2, 3] because a and b are two names for one listNone because append returns nothing[3] because append replaces the list
6. Which conversion is safe for the string "3.9" if you want a whole number of items?
int('3.9') works and yields 3float('3.9') then int(...) if truncating is acceptable — int('3.9') itself raises ValueErrorbool('3.9') yields 3str('3.9') yields 4
7. You want to loop through names in a list and print each one. Which construct is the most direct?
while True with a manual counter you might forget to incrementAn if statement with no loopfor name in namesrange() without the list
8. Why write if user is not None and user.active instead of if user.active and user is not None?
is not None is slower so it should go lastand short-circuits: if user is None, the second check never runs, so you do not access .active on NonePython requires None checks on the rightAttribute access cannot appear in if tests
9. count is 0 (a real measurement). What happens if you write if count: to mean "we have a count"?
The block runs because 0 is a numberPython raises ValueErrorThe block runs because 0 is TrueThe block is skipped because 0 is falsy, even though the measurement exists
10. You write names = names.sort(). What is names afterward?
None, because sort sorts in place and returns NoneA new sorted list, because sort always copiesThe original unsorted listA set of unique names
11. You need to know whether an order id has already been processed, among tens of thousands of ids. Which structure fits?
A string with all ids concatenatedA list you scan from the start each time onlyA set of ids (or a dict keyed by id)A float
12. Why can't a list be a dictionary key?
Lists are too long for memoryDictionary keys must be immutable/hashable; lists can change, which would break the mappingKeys may only be integersPython forbids nested data
13. A function prints a total but has no return. Another function does result = that_function(). What is result?
The printed text captured automaticallyThe last number mentioned in the functionA new empty listNone
14. Why put if __name__ == "__main__": around the code that starts your program?
So importing the file defines functions without launching the whole programBecause Python cannot define functions otherwiseTo hide the file from pipTo disable exceptions
15. def add_item(item, basket=[]): then two calls that each add one item to the default basket. What goes wrong?
The default list is created once and shared, so later calls see earlier itemsPython ignores default argumentsbasket must be a dictappend is illegal on lists

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