Popup Quiz

Please find below a set of questions representing the kind of Python required to benefit in an optimal manner from this course. If you are able to answer most of the questions without problems, you likely have a level of Python knowledge suitable for this course.

Question 1

How can you execute a Python script from a terminal?

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$ python3 myscript.py

Question 2

What is the difference between a = 3 and a == 3?

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The first statement assigns the value of 3 to the variable a as an integer. a == 3 checks if a is equal to 3.

Question 3

What is the purpose of indenting in Python? Name keywords (minimum: 8) typically leading to a subsequent indent!

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The indents are showing the different levels of nested code. Python does not use parentheses to indicate code blocks (such as for-loops).
Standard keywords with a subsequent indent are for, while, if, else, elif, with, try, except, finally, def and class.

Question 4

How can you run a loop over all odd integers from 3 up to but not including 15?

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for i in range(3,15,2): ...

Question 5

How can you run a loop over all items of the list mylist?

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for entry in mylist: ...

Question 6

When are you using for, when while?

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A for-loop is more suitable if the termination condition leads to a fixed number of iterations e.g. when iterating over the items of a list.

Question 7

Re-write the for-loop of Question 4 as a while-loop?

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i=3 while i<15: ... i += 2

Question 8

What is the difference of a set compared to a list?

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A set is a container that only contains unique items and the order of the items is not relevant.

Question 9

How do you sort a list in Python?

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sorted_list = sorted(mylist) or mylist.sort()

Question 10

And how do you sort a set?

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Since a set does not guarantee the order of its items, it is unsortable. The command sorted(myset) is valid, but returns a sorted list of the items in myset.

Question 11

How do you create in one line a Python dictionary with values from 0 to 9 and keys 'key_i' (as a string) where i stands for the square of the corresponding value?

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mydict = {'key_{}'.format(v**2) : v for v in range(10)} or mydict = {f'key_{v**2}': v for v in range(10)}

Question 12

How can you define a function that prints 'Hello, World!'?

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def helloWorld(): print('Hello, World!') Please note that print is in Python 3 a fulfledged function (Parentheses!).

Question 13

What is the difference between print and return in a function? Give an example of a function that uses both.

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print has the purpose of displaying its argument for example on the terminal. return has the purpose of handing back the result of the function to the programme. The return value can for example be stored in a variable.
def square_with_print(x): print('The square of {0:.1f} is {1:.1f}!'.format(x,x**2)) return x**2

Question 14

How do you read a text file line by line and store every line as an item in a list?

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with open('/path/to/file.txt') as f_i: mylist = f_i.readlines() # or `mylist = list(f_i)`
Please be aware that both commands keep the newline characters at the end of each line.

Question 15

How can you define in one line the function cos(x)·sin(x)?

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import math myfunc = lambda x: math.cos(x)*math.sin(x)

Question 16

How can you catch an exception, e.g. a ValueError that occurs when converting a string into an integer?

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try: i = int(s) except ValueError: print(s+' cannot be converted into an integer.') ...
The print statement is only an example of a potential code snippet.

Question 17

What does a = myfunction()[3] do?. What needs to be fulfilled for the code to be working?

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The code stores the 4th element of the return value of myfunction() in the variable a. The return value of myfunction() needs to be an object supporting access by index with key '3' set. (e.g. a list with at least four elements or a dict {3: ...})

Question 18

What do a = [], a = {} and a = () do?

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They create an empty list, dictionnary and tuple, respectively. The latest one is of questionable purpose since a tuple is immutable. While {1,2,3} creates a set, an empty set can only be initiated by set().