Python

Question 1

What does it mean that Python has dynamic types and what practical side effects are a result of that?

Answer 1

Only runtime objects have a value, not the variables themselves (that store the objects). This allows you to store different types in the same variable during execution, and means you don’t have to declare variable types when declaring them.

Question 2

Does Python have a strong or weak typing system?

Answer 2

Strong

Question 3

What does it mean that Python is strongly typed?

Answer 3

Variables won’t change types unless it is explicitly cast to something else. So ‘125’ doesn’t automatically become an int when you try to add 4 to it, even though it could be done, you would have to explicitly cast it to an int yourself.

Question 4

How to represent infinity?

Answer 4

inf = float(‘inf’) or import math, math.inf

Question 5

What does REPL stand for?

Answer 5

Read Evaluate Print Loop

Question 6

When will the code in the else condition of a for (or while) loop run?

Answer 6

If the loop completed without breaking.

Question 7

Does the “or” operator return anything? If so, what? Does it always evaluate every operand and why or why not?

Answer 7

Yes. The first truthy operand, or the last operand regardless of its truthiness. No, it will stop as soon as it finds a truthy operand which could be the first.

Question 8

Does the “and” operator return anything? If so what? Does it always evaluate every operand, and why or why not?

Answer 8

Yes, the last operand (if all were truthy) or the first non-truthy operand. No, it will stop early if it finds something non-truthy, as anything non-truthy would make the result non-truthy.

Question 9

How to get the lowercase version of a string?

Answer 9

string.lower()

Question 10

Name two ways to get environment variables w/ Python. Why is one preferred over the other?

Answer 10

os.environ[‘variable’] (will error if variable doesn’t exit) or os.getenv(‘variable’) better cause will return None if doesn’t exist, can optionally specify a default value.

Question 11

How do you open a file in python for reading and writing?

Answer 11

f = open(‘path’, mode=’r+t’) or r+b for binary, t is text

Question 12

How to open a new file in Python?

Answer 12

mode=’x’, which will error if file alread exists. ‘w’ would work but would blank out the file if it does exist.

Question 13

What can you use in Python to ensure a file is closed once operations are complete?

Answer 13

with open() as var:
stuff
Will call close if stuff fails or completes.

Question 14

How to access arguments passed to script?

Answer 14

Import sys, sys.argv. 0 is path to script. Or argparse

Question 15

What is the flow for exception handling in python?

Answer 15

Try, except - if try hit an error, else - if no error, finally - runs regardless of if hit an error or not

Question 16

What is chaining a comparison in Python? When is it preferred over non chained comparisons and why?

Answer 16

Chaining is writing 1 < x <= y instead of 1 < x and x <= 5. It is almost always preferred as it will only evaluate x once in the chained version, rather than twice in the non chained. And x is a function or calculation, that can speed things up quite a bit.

Question 17

What are the prerequisites for x in y to work?

Answer 17

y just needs to be a sequence to contains elements of type x. So even string will work, just very slow (linear time)

Question 18

How do you define a set literal?

Answer 18

{item, item, item} don’t use set(), cause it only takes one argument, so you’ll have to make a tuple inside of it or something.

Question 19

What is the ternary operator?

Answer 19

if else on one line

EXPR_1 if CONDITION else EXPR_2

Question 20

Explain LEGB

Answer 20

Order in which a variable name gets resolved.
Locals - (that aren't explicitly declared global)
Enclosing - From inner to outer (of nested functions)
Globals - Defined at top level of a module or explicitly declared global from a local scope
Built-in - Reserved keywords

Question 21

How to interact with a global variable inside a local scope?

Answer 21

To read you don’t have to do anything special cause of LEGB. To modify it you need to first declare it as global then you can modify it.

Question 22

How do you interact with an outer variable (but not global) from a nested scope?

Answer 22

Use ‘nonlocal’ keyword as you would use ‘global’. i.e. declare the variable as ‘nonlocal’, then you can modify it. No need to do this if you only want to read cause LEGB.

Question 23

How do you clean up the ends of a string?

Answer 23

lstrip, rstrip, strip (head and tail). Each take one arg, a string, every character in the string will be stripped. Continues stripping until encounters a character not in the strip string. without an arg strips all whitespace.

Question 24

How far in will lstrip and rstrip go?

Answer 24

Until they hit a char not in the stripping string. Order doesn’t matter.

Question 25

How would you filter/process a string without creating a new string in memory, and then print it out?

Answer 25

Use a generator comprehension. Then print it out as ‘‘.join(generator)

Question 26

What arguments does split() take?

Answer 26

First is string to split on, whitespace by default, then maxsplit=n is how many times to split.

Question 27

What is calling multiple methods on an object at once called? Give an example.

Answer 27

Chaining

str.lower().replace(‘!’)k

Question 28

What is the return type of / in Python? Always?

Answer 28

Float, yes.

Question 29

Where should whitespce go when using : in Python?

Answer 29

If not at the end of a line (for if thing:) then it’s no space before but space after. So like my_dict = { ‘hi’: ‘bye’}

Question 30

How can you make large numeric literals easier to read? Where is this supported?

Answer 30

Since python 3.6 can use _ which has no meaning. So 100,000 can be written 100_000.

Question 31

How to get a random integer in Python?

Answer 31

random. randrange() works like range

random. randint() inclusive range a to b parameters

Question 32

How to get a random element from a sequence in Python? How would you get x random elements from that sequence?

Answer 32

random. choice(seq)

random. sample(sequence, x)

Question 33

How to put a sequence in random order?

Answer 33

random.shuffle(seq)

Doesn’t work on immutable sequences

Question 34

How do you get an attribute of an object, if the attribute name is stored as a string?

Answer 34

getattr(object, attr_name_str)

OR

object.__getattribute__(name_str)

Question 35

What are the two ways to call an instance method?

Answer 35

self.method() or Class.method(self)

Question 36

How do you reference a Class as a type (for type hinting) within the definition of its methods?

Answer 36

Just using Class name won’t work as it isn’t fully define. Can put it within string literals.