Code Cell#

You can write and execute Python code in code cells.

  • An arrow on the left of a code cell allows you to run the code.

  • Additionally, you can use the shortcut Shift+Enter to execute the code.

  • A number in a square bracket on the left of executed code cells represents the execution order of that code cell.

  • Warning: The order of a code cell in the notebook and its execution order can differ if you run another code cell above it

Numbers#

  • You can use integers (…,-3,-2,-1,0,1,2,3,….) and decimal numbers called floats in a code cell.

Algebraic Operations#

  • You can perform algebraic operations in code cells.

  • The multiplication operator is * (asterisk).

  • The division operator is / (forward slash).

  • The exponent operator is ** (double asterisk).

print(5+9)

14

print(10.4-4.5)

5.9

print(5*6)

30

print(10/2)

5.0

print(2**3)

8

Strings#

  • Strings are sequences of characters.

  • They can be written inside single quotes, double quotes, triple single quotes, or triple double quotes.

print('Hello')

Hello

print("Hello")

Hello

print('''Hello''')

Hello

print("""Hello""")

Hello

'3'   # string '3 'is not a number, it is only a character

'3'

# ERROR: you are trying to add a string (character) '3' and a number (5) 
'3'+5

String Operations#

  • String + String: combines two strings

  • String * Integer or Integer * String: makes copies of the string Integer many times.

# concatenation: combining two strings
print('Hello' + 'World')

HelloWorld

# repetition: # 10 Ms
print('M'*10)

MMMMMMMMMM

Booleans#

  • There are only two boolean values: True and False.

  • They indicate whether a condition is valid or not.

  • Booleans will be covered in Conditionals chapter with details.

Comments#

  • Use # to add notes to your program, explaining the purpose of the code.

  • Comments are not executed but serve as explanations.

  • Additionally, you can place comments to the right of the code.

  • Comments make the code easier to read and understand.

  • Comments help team members understand each other’s code.

# this is a comment: addition
print(2+8)

10

print(2+8)  # addition

10

Built-in functions#

  • There are functions readily available for use in a notebook.

  • There is no need to import these built-in functions from external sources.

  • You can find the list of built-in functions in the following link.

# absolute value function
print(abs(-7))

7

# maximum of a list of numbers
print(max(3,-4,0,9,2))

9

# minimum of a list of numbers
print(min(3,-4,0,9,2))

-4

# sum of a list of numbers in a square bracket
print(sum([3,5,2]))

10

# rounding to the nearest hundredth
print(round(3.4678, 2))

3.47

# notebook only displays the value in the last line of the code cell
5-1  # not displayed
3+7  # displayed

10

# print() displays the outputs
print(5-1)  #  displayed
print(3+7)  # displayed

4
10

Indentation#

  • Indentation refers to the spaces at the beginning of a code line.

  • Python uses indentation to indicate a block of code.

  • Do not use indentation unless you need it.

  • Indentation refers to the spaces at the beginning of a code line.

  • Python uses indentation to group the block of code.

  • Only use indentation when necessary.

# ERROR: Indentation error
# There should not be space at the beginning
print(3+1)
 print(5+6)

Import Modules/Packages/Libraries#

  • Only very commonly used, simple functions are available in a notebook by default.

  • Python has a vast set of modules, packages and libraries where one can find numerous functions.

  • For instance, the mean() function is not available by default in a notebook.

# ERROR: 'mean' is not defined
mean(4,8)

  • The mean function can be imported from the statistics module or numpylibrary.

  • You can import a package and call any function from it using the package.method.

  • You can import only the function(s) you need from the package using the from PACKAGE import METHOD.

  • Additionally, you can import a package and rename it for shorter usage by employing the import PACKAGE as ABBREVIATION.

import statistics        # import whole module
statistics.mean([4,8])   # call mean method from statistics module

6

from statistics import mean        # import only mean method
mean([4,8])                        # call mean method 

6

import statistics as st        # import whole statistics module as st
st.mean([4,8])                 # call mean method from st module

6

import numpy as np        # import numpy package as np
np.mean([4,8])            # call mean method from np package

6.0

  • You can call mathematical constants and functions from the math module.

  • Functions in modules are also referred to as methods.

  • The built-in dir() and help() functions display the lists of constants (attributes) and functions (methods).

# displays all functions and constants in math module
import math
dir(math)

# displays all functions and constants in math module with explanation
import math
help(math)

import math
print(dir(math))

['__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'cbrt', 'ceil', 'comb', 'copysign', 'cos', 'cosh', 'degrees', 'dist', 'e', 'erf', 'erfc', 'exp', 'exp2', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'inf', 'isclose', 'isfinite', 'isinf', 'isnan', 'isqrt', 'lcm', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'nextafter', 'perm', 'pi', 'pow', 'prod', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau', 'trunc', 'ulp']

print(math.pi)

3.141592653589793

# ln(10)
print(math.log(10))   # natural log 10

2.302585092994046

  • The datetime module contains methods that can be used for working with time and date

import datetime
print(datetime.datetime.now())    # date and time now

2024-09-14 07:17:01.872626

  • You can use the calendar module to display a monthly calendar.

import calendar                   # import calendar module
print(calendar.month(1900, 1))    # display Jan month of 1900

    January 1900
Mo Tu We Th Fr Sa Su
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31

  • You can use the randommodule to generate random numbers or make random choices.

import random
random.randint(1,10)  # choose a random integer between 1 and 10

3

random.choice(['a','b','c'])  # choose a random element from a list

'c'

Magic Methods#

  • The methods in dir(math) enclosed by double underscores __ are referred to as magic functions.

  • These functions operate in the backend and are not intended for direct user use.

  • While it is still possible to use them, there is usually a more user-friendly alternative.

  • For example, if you examine dir(int), you will find the __add__ method, which handles the addition operation internally, corresponding to the use of the + operator.

number = 3
print(number + 5)
print(number.__add__(5))  # same as 3+5

8
8

Images#

  • You can import images from a website using the IPython library.

  • Adjust the size of the image by utilizing width and height parameters.

from IPython.core.display import Image
Image('https://www.python.org/static/community_logos/python-powered-h-100x130.png',width=100,height=100)
_images/0e440193a7b074e7f072edfa1a2e85af0d9b6b26f50f388d88da73df50627c92.png

Youtube Video#

  • You can import YouTube videos using the unique ID number.

  • The ID number of a YouTube video can be found in the video’s URL directly after the = sign

  • ID number of https://www.youtube.com/watch?v=rNgswRZ2C1Y is rNgswRZ2C1Y

from IPython.lib.display import YouTubeVideo
YouTubeVideo('rNgswRZ2C1Y', width=800, height=300)