Chapter 4: Programming in Python

print("Hello, Nepal!")
print("Welcome to Python programming.")

name = "Sita"        # text (string)
age = 16             # whole number (int)
height = 5.4         # decimal number (float)
is_student = True    # True/False (bool)

print(name, age, height, is_student)

name = input("Enter your name: ")
age = int(input("Enter your age: "))   # convert text to number

print("Hello", name)
print("Next year you will be", age + 1)

name = "Sita"
marks = 92

# f-string (recommended)
print(f"{name} scored {marks} marks.")

# .format() method
print("{} scored {} marks.".format(name, marks))

a = 10
b = 3
print(a + b, a % b, a ** b)        # arithmetic
print(a > b, a == b)               # relational
print(a > 5 and b < 5)             # logical

marks = int(input("Enter your marks: "))

if marks >= 90:
    print("Grade A+")
elif marks >= 60:
    print("Grade A")
elif marks >= 40:
    print("Pass")
else:
    print("Fail")

for i in range(1, 6):
    print("Number:", i)

count = 1
while count <= 3:
    print("Hello", count)
    count = count + 1

fruits = ["apple", "banana", "orange"]

print(fruits[0])        # first item
print(fruits[-1])       # last item

fruits[1] = "mango"     # change an item
print(fruits)

marks = [55, 90, 70, 40]

print("Count:", len(marks))
print("Total:", sum(marks))
print("Highest:", max(marks))
print("Lowest:", min(marks))

marks.append(100)        # add at end
marks.insert(0, 25)      # add at start
print(marks)

student = {
    "name": "Sita",
    "age": 16,
    "class": 10
}

print(student["name"])      # get value by key
student["age"] = 17         # change a value
student["city"] = "Pokhara" # add new pair
print(student)

student = {"name": "Ram", "age": 15, "class": 10}

print(student.get("name"))
print(student.keys())
print(student.values())

del student["age"]
print(student)

text = "Technology Channel"
print(text.upper())
print(text.lower())
print("Length:", len(text))
print("Number of 'n':", text.count("n"))
print(abs(-10), pow(2, 5), hex(255))

def add(a, b):        # def + name + parameters
    result = a + b
    return result     # return type

answer = add(5, 3)    # function call
print("Sum is", answer)

def greet(name):       # 'name' is a PARAMETER
    print("Namaste,", name)

greet("Sita")          # "Sita" is an ARGUMENT
greet("Ram")

school = "ABC School"     # GLOBAL variable

def show():
    msg = "Welcome"      # LOCAL variable
    print(msg, "to", school)

show()
print(school)            # works (global)
# print(msg)             # ERROR: msg is local

def square(n):
    return n * n

print(square(4))     # uses the returned value

def greet():
    print("Hello!")   # just does a job, returns nothing

greet()

def calc(a, b):
    return a + b, a - b, a * b   # returns three values

total, diff, product = calc(10, 4)
print(total, diff, product)

def student(name, country="Nepal"):   # country has a DEFAULT
    print(name, "-", country)

student("Sita")                    # positional
student("Ram", "India")            # positional override
student(country="USA", name="Gita")  # keyword arguments

pip install numpy
pip install pandas matplotlib

# 1. Import the whole module
import math
print(math.sqrt(25))

# 2. Import a specific function from a module
from math import sqrt
print(sqrt(36))

# 3. Import with a short nickname (alias)
import math as m
print(m.pi)

import math

print(math.sqrt(49))        # square root  -> 7.0
print(math.pow(2, 4))       # power        -> 16.0
print(math.factorial(5))    # 5! = 120
print(math.gcd(12, 18))     # GCD          -> 6
print(math.log(100, 10))    # log base 10  -> 2.0

import random

print(random.randint(1, 6))                  # like rolling a dice
print(random.choice(["Ram", "Sita", "Gita"])) # pick one randomly

import pandas as pd

data = {"Name": ["Ram", "Sita"], "Marks": [80, 95]}
df = pd.DataFrame(data)
print(df)

import turtle

pen = turtle.Turtle()

# draw a square
for i in range(4):
    pen.forward(100)   # move 100 steps
    pen.right(90)      # turn 90 degrees

turtle.done()

import matplotlib.pyplot as plt

subjects = ["Maths", "Science", "English"]
marks = [85, 92, 78]

plt.bar(subjects, marks, color="teal")
plt.title("My Marks")
plt.xlabel("Subject")
plt.ylabel("Marks")
plt.show()

import matplotlib.pyplot as plt

x = [1, 2, 3, 4, 5]
y = [10, 14, 9, 18, 20]

plt.scatter(x, y, color="red")
plt.title("Scatter Plot Example")
plt.show()

try:
    num = int(input("Enter a number: "))
    print("100 divided by your number is", 100 / num)
except ZeroDivisionError:
    print("Error: cannot divide by zero!")
except ValueError:
    print("Error: please type a valid number!")

f = open("notes.txt", "w")
f.write("Hello from Python!\n")
f.write("This is line two.")
f.close()
print("File saved.")

f = open("notes.txt", "r")
content = f.read()
f.close()
print(content)

f = open("notes.txt", "a")
f.write("\nA new line added later.")
f.close()

import os
os.remove("notes.txt")
print("File deleted.")

import csv

with open("students.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Marks"])   # header row
    writer.writerow(["Ram", 80])
    writer.writerow(["Sita", 95])

print("CSV written.")

import csv

with open("students.csv", "r") as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)

def grade(total):
    if total >= 90:
        return "A+"
    elif total >= 60:
        return "A"
    elif total >= 40:
        return "Pass"
    else:
        return "Fail"

students = []

for i in range(2):
    name = input("Enter student name: ")
    marks = int(input("Enter total marks: "))
    students.append({"name": name, "marks": marks, "grade": grade(marks)})

print("\n----- RESULT -----")
for s in students:
    print(f"{s['name']}: {s['marks']} marks -> Grade {s['grade']}")