Python

Question 1

Why do long integers take longer to process in Python than in most other languages?

Answer 1

Because they are stored internally as an array of digits.

Question 2

What is the difference between double quoted strings and single quoted strings in python?

Answer 2

There is no difference.

Question 3

Are escape characters valid in Python?

Answer 3

Yes.

Question 4

How are invalid escape characters treated in Python?

Answer 4

They treated like regular text.

Question 5

How can escape characters be turned off in Python?

Answer 5

By prefacing the string with an r (to specify a raw string).

Question 6

Do multi line strings require triple single-quotes or triple double-quotes?

Answer 6

Either.

Question 7

When does the interpreter automatically add new line characters to multi line strings?

Answer 7

Always, unless the line ends in a backslash.

Question 8

Does prefacing a multi line string in python with ‘r’ prevent the interpreter from adding new line characters?

Answer 8

No.

Question 9

Does python provide bounds checking for when indexing strings?

Answer 9

Yes.

Question 10

What is the output of the following?
x = “carlisle”
print(x[2:3])

Answer 10

r
(since slices use inclusive/exclusive format)

Question 11

What is the output of the following?
x = “car”
print(x[::-1])

Answer 11

rac

Question 12

What is the output of the following?
x = “bugman”
print(x[2:44])

Answer 12

gman
(valid, despite apparent out of bounds)

Question 13

What is the output of the following?
x = “bugman”
x[2] = “s”
print(x)

Answer 13

This issues an error, since strings are immutable in Python.

Question 14

Is the following valid, where x is a list of length 4?
print(x[2:99])

Answer 14

Yes.

Question 15

How are lists in Python implemented at the memory level?

Answer 15

As dynamically resized arrays of pointers.

Question 16

Why aren’t lists in Python implemented as linked lists at the memory level?

Answer 16

Because operations on linked lists (especially indexing) is much too slow.

Question 17

What is the asymptotic complexity of accessing / updating a list element by index?

Answer 17

O(1)

Question 18

What is the asymptotic complexity of appending to a list?

Answer 18

O(1) if space is available, O(n) otherwise.

Question 19

What is the asymptotic complexity of inserting into a list?

Answer 19

O(n)

Question 20

What is the asymptotic complexity of building a list by inserting every element into the first position?

Answer 20

O(n^2)

Question 21

How can you attempt to access a key’s value in a dictionary, without raising a KeyError exception should that key not exist?

Answer 21

By using dict.get(key), over dict[key].

Question 22

What is the (amortized) cost of a lookup in a dictionary?

Answer 22

O(1), as there is a constant number of steps in executing the hash function.

Question 23

How are tuples of 1 element created?

Answer 23

With a trailing comma.

Question 24

What are the 2 primary differences between sequences and sets in python?

Answer 24

Unlike sequences, sets are unordered and do not allow duplicates.

Question 25

How do you initialize an empty set in python?

Answer 25

Using the set() function, since {} creates an empty dictionary.

Question 26

How do sets prevent duplicates?

Answer 26

By being internally implemented as a hash table.

Question 27

Does adding an element that already exists to a set cause an error?

Answer 27

No, the duplicate value is simply not inserted.

Question 28

Why must set elements be immutable in python?

Answer 28

Because they must be hashable, as the underlying data structure is a hash table.

Question 29

4 spaces can always be used in place of tab characters for delimiting coding blocks.

Answer 29

It is generally recommended to use 4 spaces over a tab, but never use both techniques in the same source file.

Question 30

Which data types can follow the “in” keyword?

Answer 30

Sequences.

Question 31

A value of NULL is assigned to all uninitialized variables.

Answer 31

False. Variables meant to be defined later must be explicitly set equal to ‘None,’ which is Python’s equivalent to Null.

Question 32

Functions return void by default.

Answer 32

False, they return None by default.

Question 33

When are module imports handled in Python, and when are include directives handled in C?

Answer 33

In C, extended code is converted into object code at compile time, whereas the Python import process occurs at run time.

Question 34

For what files does the Python interpreter create .pyc files?

Answer 34

Only for imported modules, and not for the main script.

Question 35

A module may be imported more than once.

Answer 35

A module may be subject to multiple import statements, but the interpreter will not physically import a module more than once.

Question 36

Which environment allows developers to add their own folders to the module search path?

Answer 36

PYTHONPATH
(similar to Java’s CLASSPATH)

Question 37

How do Python global variables and C global variables differ?

Answer 37

Python global variables aren’t global to all modules, unless imported.

Question 38

When can you not use the ‘global’ keyword to access a global variable from within a function?

Answer 38

If a local variable of the same name has already been declared.

Question 39

If mod_name is the name of a module, when does the following code fail?
dir(mod_name)

Answer 39

When mod_name hasn’t been imported.

Question 40

When is the __name__ global variable not accurately set to the name of the current module?

Answer 40

When the current module represents the starting module for the application, in which case __name__ is set to “__main__”.

Question 41

How can a package be defined such that only 1 of its modules it imported when “from package import *” is called.

Answer 41

__all__ = [“module_name”] must be included in the packages __init__.py file.