Keywords

Question 1

Name four scenarios where as keyword is used.

Answer 1

• To create an alias for module name in import statement.
• To create an alias for sub-module name in import statement.
• To create an alias for resource in with resource statement.
• To create an alias for exception.

Question 2

What’s the syntax for creating an alias for exception with as keyword?

Answer 2

except <exception_name> as <alias_name>

Question 3

Does assert throw an error when the following condition is true or false?

Answer 3

When the condition is false.

Question 4

What’s the syntax for assert in python?

Answer 4

assert condition, message

Question 5

What’s the purpose of the del keyword in python?

Answer 5

del is used to delete the reference to an object. Ex:

>>> a = b = 5
>>> del a
>>> a
Traceback (most recent call last):
  File "<string>", line 301, in runcode
  File "<interactive input>", line 1, in <module>
NameError: name 'a' is not defined
>>> b
5

Question 6

What’s the syntax for try except blocks in python?

Answer 6

try:
    # Some code
except <Exception>:
    # Run on <Exception>
except:
    # It's possible to put more than one except block under one try 
    # block, and you don't need to specify the <Exception> after the 
    # except keyword

Question 7

What’s the syntax for the raise keyword in python?

Answer 7

if num == 0:
    raise ZeroDivisionError('cannot divide')

Question 8

What’s the purpose of the finally keyword?

Answer 8

finally is used with try…except block to close up resources or file streams.

Using finally ensures that the block of code inside it gets executed even if there is an unhandled exception.

Question 9

What are the two uses for the global keyword?

Answer 9

• To create a global variable inside a function
• To modify a global variable inside a function

Question 10

What’s the use of the in and not in keywords?

Answer 10

in is used to test if a sequence (list, tuple, string etc.) contains a value. It returns True if the value is present, else it returns False. not in works equivalently.

Question 11

Can in and not in only be used with sequence data structures like lists or sets?

Answer 11

No, it can also be used with generators like range()

Question 12

What’s the use of the is keyword in python?

Answer 12

is is used in Python for testing object identity. While the == operator is used to test if two variables are equal or not, is is used to test if the two variables refer to the same object.

Question 13

What’s the syntax for an anonymous function in python?

Answer 13

lambda a: a**2

Question 14

What’s the difference between the nonlocal keyword and the global keyword?

Answer 14

The difference is that the nonlocal keyword is used only with variables outside the local scope, like for example variables declared in outer function, but not with global variables.

Question 15

What’s the syntax for the with statement?

Answer 15

with expression as target_var:
    do_something(target_var)

Question 16

Is the is keyword required in with statements?

Answer 16

No, the short version of the with statement is:

with expression:
    do_something(expression)

Question 17

Can you use only one context menager with one with statement?

Answer 17

No, you can use multiple context menagers with one with statement and separate them with commas:

with A() as a, B() as b:
    pass

Question 18

How does the yield keyword work, and what is a generator?

Answer 18

yield is used inside a function like a return statement. But yield returns a generator.

Introduced withPEP 255, generator functionsare a special kind of function that return a lazy iterator. These are objects that you can loop over like a list. However, unlike lists, lazy iterators do not store their contents in memory.

While using yield instead of return the state of the function is preserved and the next time the generator function (the function with yield) is called the execution resumes from the next line after yield statement.

Question 19

What’s the syntax for generator comprehension?

Answer 19

csv_gen = (row for row in open(file_name))

Question 20

What are the three ways to use a generator?

Answer 20

Create an object:
generator = gen()

for i in generator:
pass
Use as is:
for i in gen():
pass
Use a special function:
next(gen())

Question 21

Can the yield keyword be used in a expression?

Answer 21

Yes, the yield keyword can be used in an expression and then after the execution stops, the .send() method can be used to send the value to the generator:

>>> def double_inputs():
...     while True:
...         x = yield    # yield can also be used as an expression
...         yield x * 2
...
>>> gen = double_inputs()
>>> next(gen)       # run up to the first yield
>>> gen.send(10)    # goes into 'x' variable

Question 22

How to stop a generator?

Answer 22

There are two ways to stop a generator, using the .throw() method and .close() method. Both work in similar ways, but with the .throw() method its possible to pass an error to the generator:

>>> def double_inputs():
...     while True:
...         x = yield    # yield can also be used as an expression
...         yield x * 2
...
>>> gen = double_inputs()
>>> next(gen)       # run up to the first yield
>>> gen.send(10)    # goes into 'x' variable