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Question 1

How to install pip3 in Ubuntu?

Answer 1

sudo apt-get install python3-pip

Question 2

How to install PyQt5 on Ubuntu?

Answer 2

sudo -H python3 -m pip install pyqt5

Question 3

Python: if an instance method is called with three arguments, how will the method signature look?

Answer 3

Signature will have four arguments, with ‘self’ being the first argument.

Question 4

Python: How are ‘class methods’ defined?

Answer 4

They are decorated with @classmethod.
First argument in their signature is ‘cls’ representing the class, NOT an instance/self.

Question 5

Python: What are ‘static methods’?

Answer 5

These are decorated with @staticmethod. Arguments at the time of calling and method signature exactly match. No ‘self’ or ‘cls’ argument is implicitly passed.

Question 6

Python: What is an ‘iterable’?

Answer 6

Iterable is a sequence data structure, like a list, tuple etc.

Question 7

Python: Write generator for even numbers less then 20

Answer 7

(i for i in range(20) if i%2 == 0)

Question 8

Python: Can a generator be used again, after it is made use of?

Answer 8

No, once you iterate over a generator, you must define it again, if you want to use it again.

Question 9

Python: What are instance attributes and class attributes?

Answer 9

Instance attributes are different for each object, they are always accessed as self.attr_name inside the class definition. They are most common kind of attributes.

Class attributes are shared by all objects of a class. They are normally declared outside __init__ xtor, without self.
Inside methods, class attributes are referred with self.attr_name, just like instance attributes.

Question 10

What is special about class ‘object’ in python?

Answer 10

Every class in python is derived from ‘object’ class.

Question 11

Python: What happens when you assign an object to another variable?

Answer 11

New variable name is a new reference to original object.
Any change in original object will be visible through the new variable.

Question 12

Python: How to add an item at the end of a list?

Answer 12

lst.append(“new item”)

Question 13

Python: How to remove an item from an index of a list?

Answer 13

removed_item = lst.pop(index)
lst.pop() without an argument will remove last item.

Question 14

Python: How is dir() used with modules?

Answer 14

After importing a module mode, dir(mod) gives all new symbols added by mod.

dir() without any arguments gives list of all global names known.

Question 15

What is a python module?

Answer 15

It is a regular python code file. It can be imported in another file, that way making variables defined in the module file become available here.

Question 16

What is a python package?

Answer 16

A python package is a directory containing multiple module files.

from pkg_dir import module_file_1

pkg/modules are addressed like directory structure.
pkg/sub_pkg/module_file
import pkg.sub_pkg.module_file

Package directory can contain an __init__.py file

Question 17

Python: What happens when you append b in front of a string, like b’ABCD1234’

Answer 17

In Python3, without b, each character in the string maybe represented by 16 or 32 bits, but with b in front, each character in the string is represented like old fashioned 8 bit character.

We should use b in front of string if we have to send the string over a serial line.

Question 18

Python: What module is used to do multithreading?

Answer 18

import threading

Question 19

Python: How to find the length of a list?

Answer 19

len(list_name)

Question 20

What is the diff between
pip install django and
pip –user install django

Answer 20

without –user, pip installs a package on a system wide global location. With –user pip installs the package somewhere in the user’s home directory.

Instead of using –user, a better way is to use virtual environment, & not use –user.

Question 21

Python: How to list all packages installed?

Answer 21

pip list

Question 22

Python: How to get info about an installed package?

Answer 22

pip show django

Question 23

Python: How to search PyPI.org repository for a package?

Answer 23

pip search pyqt

Question 24

Python: How to uninstall a package?

Answer 24

pip3 uninstall flask

Question 25

Python: How to get a snapshot of all packages installed in a system.

Answer 25

pip freeze > requirements.txt

These packages can be installed in another system with,

pip install -r requirements.txt

Question 26

Python: After importing a module, how to find its path in file system?

Answer 26

import mod
mod.__file__

Question 27

Python: How to find all variables (names) known?

Answer 27

dir()

returns a list of strings.

Question 28

Python: How to find all variables (names) provided by an imported module?

Answer 28

import mod
dir(mod)

returns a list of strings.

Question 29

Python: How to find type of a variable?

Answer 29

type(var_name)

print( type(var_name) )

Question 30

Python: How do u define a complex number?

Answer 30

z = 3.14 + 2.71j

– or –

z = complex(3.14, 2.71)

type(z) = < class ‘complex’ >

complex(3) = 3 + 0j
complex() = 0 + 0j

Question 31

Python: Real & imaginary parts of a complex number z?

Answer 31

z.real
z.imag

Question 32

Python: Conjugate of a complex number z?

Answer 32

z.conjugate()

Question 33

Python: Absolute value of a complex number z?

Answer 33

abs(z)

Question 34

How to create a numpy array

Answer 34

Use numpy array() function.

import numpy as np
arr = np.array([13, 17, 19, 23])

Question 35

What is the type of numpy array?

Answer 35

numpy.ndarray

Question 36

How to find number of dimensions in a numpy array arr?

Answer 36

arr.ndim

Question 37

How to access elements in a 2-dim numpy array?

Answer 37

arr[3, 7]

Question 38

How to find all dimensions of a numpy array, arr?

Answer 38

arr.shape

Question 39

numpy: how does numpy.random.randint() function work?

Answer 39

With two arguments:
np.random.randint(low, high) # Returns a random number between low and high.

With three arguments:
np.random.randint(low, high, size=(4, 8))
Returns a 4x8 array of random nums

Question 40

numpy: How does numpy.random.randn() function work?

Answer 40

np.random.randn(5)
Returns an ndarray of 5 normally distributed nums.

np.random.randn(4, 8)
Returns a 2-D ndarray size (4, 8)

Normal distribution: Mean 0, variance 1

Question 41

How is a numpy ndarray stored in a file?

Answer 41

arr.tofile(‘abc.data’)
Type of data is inferred from type(arr[0]). This data type must be used while reading the file using numpy.fromfile() function.

Read a numpy ndarray from a file
np.fromfile(‘abc.data’, np.int64)
other types might be np.float64, np.complex128, np.complex64 etc.

Question 42

numpy: how are min/max/mean/abs of a numpy.array([])

Answer 42

import numpy as np
arr = np.array([101, 102, 103])

np.min(arr)
np.max(arr)
np.mean(arr)
np.abs(arr)

These functions can also be used with regular python lists.

Question 43

numpy: How to convert each element of an ndarray from complex128 to complex64?

Answer 43

Let arr_1 is of complex128 type.

arr_2 = arr_1.astype(np.complex64)

Question 44

anaconda: Create a virtual env with name env39 and python version 3.9

Answer 44

conda create –name env39 python=3.9

Question 45

anaconda: List all virtual environments

Answer 45

conda env list

Question 46

anaconda: How to install a module?

Answer 46

google: “conda install flask”. Use command from https://anaconda.org

conda install -c anaconda flask

Question 47

anaconda: How to remove a module?

Answer 47

conda remove pygame

Question 48

numpy: How does arange() work?

Answer 48

new_arr = np.arange(start, stop, step)
stop is excluded

default value of step is 1

np.arange(5)
array([0, 1, 2, 3, 4])

Question 49

np: How to create an ndarray?

Answer 49

use an existing regular python list.

lst_1 = [1, 3, 5, 7]

nd_arr1 = np.array(lst_1)

– or –

arr = np.array([1, 2, 3, 4 , 5])

arange is useful when interval is given, it is NOT calculated from end-points and number of elems.