Chapter 4: Programming in Python

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

name = "Sita"        # text        -> str
age = 16             # whole number -> int
height = 5.4         # decimal      -> float
is_student = True    # True / False -> bool

print(name, age, height, is_student)
print(type(age))     # ask Python what type it is

balance = 500        # eSewa balance
print("Before:", balance)

balance = balance - 120   # bought a recharge card
print("After:", balance)

name = input("Enter your name: ")
age = int(input("Enter your age: "))    # text -> number

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

plates = int(input("How many plates of momo? "))
rate = 180

total = plates * rate
print("Total bill: Rs.", total)

name = "Sita"
marks = 92

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

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

# 3. maths works inside the braces too
print(f"Out of 100, {name} lost {100 - marks} marks.")

total = 247
percent = total / 3

print(f"Percentage: {percent}")        # ugly
print(f"Percentage: {percent:.2f}%")   # 2 decimal places

english = 72
math = 35

print(english >= 40 and math >= 40)   # passed BOTH subjects?
print(english >= 40 or math >= 40)    # passed AT LEAST one?
print(not (math >= 40))               # failed math?

score = 10
score += 5      # same as: score = score + 5
score -= 3      # same as: score = score - 3
print(score)

subjects = ["Nepali", "English", "Math"]
print("Math" in subjects)          # membership
print("Science" not in subjects)

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")

age = 18

if age >= 18:
    print("You can vote.")      # inside the if  (4 spaces)
    print("Bring your ID.")     # also inside
print("Program finished.")      # outside, runs always

# The 7 times table
for i in range(1, 6):
    print(f"7 x {i} = {7 * i}")

students = ["Sita", "Ram", "Gita"]

for student in students:
    print("Present:", student)

balance = 500

while balance >= 180:
    balance = balance - 180
    print("Bought 1 plate of momo. Left: Rs.", balance)

print("Not enough money now. Rs.", balance)

for i in range(1, 11):
    if i == 4:
        continue      # skip just this one
    if i > 6:
        break         # stop the loop completely
    print(i, end=" ")

marks = [55, 90, 70]                   # list  - can change
birth = (2065, 7, 12)                  # tuple - fixed forever
student = {"name": "Ram", "age": 15}   # dictionary
rolls = {5, 8, 5, 12}                  # set   - duplicate 5 removed

print(marks, birth, student, rolls)

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

print(fruits[0])        # first item
print(fruits[-1])       # last item (counting backwards)
print(fruits[0:2])      # slice: index 0 and 1, NOT 2

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

marks = [55, 90, 70, 40]

print("Subjects :", len(marks))
print("Total    :", sum(marks))
print("Highest  :", max(marks))
print("Lowest   :", min(marks))
print("Average  :", sum(marks) / len(marks))

marks.append(100)       # a new subject result arrived
marks.sort()            # arrange smallest to largest
print(marks)

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

print(student["name"])        # read a value using its key
student["age"] = 17           # change a value
student["city"] = "Pokhara"   # add a brand-new pair
print(student)

phonebook = {
    "Aama": "9841000001",
    "Buwa": "9841000002",
    "School": "014400000"
}

who = "Buwa"
print(f"{who}'s number is {phonebook[who]}")

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

print(student.get("name"))
print(student.get("address"))     # missing key -> None, no crash
print(student.keys())
print(student.values())
print("Pairs:", len(student))

del student["age"]
print(student)

marksheet = {"Nepali": 78, "English": 65, "Math": 92}

for subject, mark in marksheet.items():
    print(f"{subject:10} : {mark}")

print("Total:", sum(marksheet.values()))

text = "Technology Channel"

print(text.upper())
print(text.lower())
print("Length:", len(text))
print("Number of 'n':", text.count("n"))
print(text.replace("Channel", "Nepal"))
print(text.split(" "))

full_name = "  Sita   Sharma  "

clean = full_name.strip().lower().replace("   ", "_")
print("Username:", clean)

print(abs(-7))        # absolute (always positive)
print(pow(2, 5))      # 2 to the power 5
print(round(3.678, 2))# round to 2 decimals
print(hex(255))       # decimal to hexadecimal

marks = [80, 95, 60]

print(sum(marks))            # LIBRARY function

def total_with_bonus(m):     # USER-DEFINED function
    return sum(m) + 5

print(total_with_bonus(marks))

def add(a, b):          # 1 & 2: def + name + parameters
    result = a + b
    return result       # 3: return the answer

answer = add(5, 3)      # 4: function call
print("Sum is", answer)

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

print("Sita:", grade(92))
print("Ram :", grade(35))
print("Gita:", grade(74))

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

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

school = "Shree Janata School"     # GLOBAL

def show():
    msg = "Welcome"                # LOCAL
    print(msg, "to", school)       # global can be read here

show()
print(school)                      # works
# print(msg)                       # ERROR: msg does not exist here

def square(n):
    return n * n

area = square(4)      # the returned value is stored
print(area)

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

x = greet()
print("Returned value:", x)

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

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 (default used)
student("Ram", "India")               # positional (default replaced)
student(country="USA", name="Gita")   # keyword, order changed

pip install numpy
pip install pandas matplotlib

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

# 2. Import one specific function from it
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
print(math.pow(2, 4))       # power
print(math.factorial(5))    # 5! = 5x4x3x2x1
print(math.gcd(12, 18))     # greatest common divisor
print(math.ceil(4.1))       # round UP
print(math.floor(4.9))      # round DOWN

import random

print(random.randint(1, 6))                    # roll a dice
print(random.choice(["Ram", "Sita", "Gita"]))  # pick a name

names = ["Ram", "Sita", "Gita"]
random.shuffle(names)                          # mix the order
print(names)

import datetime

today = datetime.date.today()
print("Today is:", today)
print("Year:", today.year)

import pandas as pd

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

print(df)
print("Average marks:", df["Marks"].mean())

import turtle

pen = turtle.Turtle()

# Draw a square: 4 sides, turning 90 degrees each time
for i in range(4):
    pen.forward(100)
    pen.right(90)

turtle.done()

import matplotlib.pyplot as plt

subjects = ["Nepali", "Math", "Science"]
marks = [78, 92, 85]

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

import matplotlib.pyplot as plt

months = ["Baisakh", "Jestha", "Asar", "Shrawan"]
sales = [1200, 1500, 900, 1800]

plt.plot(months, sales, marker="o")
plt.title("Shop Sales")
plt.ylabel("Rs.")
plt.show()

import matplotlib.pyplot as plt

labels = ["Study", "Sleep", "Play", "Other"]
hours = [8, 8, 3, 5]

plt.pie(hours, labels=labels, autopct="%1.0f%%")
plt.title("My Day in 24 Hours")
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!")
finally:
    print("Thank you for using this program.")

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()

print(open("notes.txt").read())

import os

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

with open("diary.txt", "w") as f:
    f.write("Aaja Python sikeko din.")
# file closes automatically here

with open("diary.txt", "r") as f:
    for line in f:
        print(line)

Name,Marks
Ram,80
Sita,95

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)

import csv

total = 0
with open("students.csv", "r") as f:
    reader = csv.reader(f)
    next(reader)                 # skip the header row
    for row in reader:
        total = total + int(row[1])

print("Total marks:", total)

def grade(percent):
    if percent >= 90:
        return "A+"
    elif percent >= 80:
        return "A"
    elif percent >= 60:
        return "B"
    elif percent >= 40:
        return "C"
    else:
        return "Fail"

print(grade(92), grade(64), grade(31))

students = []

for i in range(2):
    name = input("Student name: ")
    nepali = int(input("Nepali marks: "))
    english = int(input("English marks: "))
    math = int(input("Math marks: "))

    total = nepali + english + math
    percent = total / 3

    students.append({
        "name": name,
        "total": total,
        "percent": percent,
        "grade": grade(percent)
    })

print("\n------ RESULT SHEET ------")
for s in students:
    print(f"{s['name']:10} {s['total']:4}  {s['percent']:6.2f}%  {s['grade']}")

topper = max(students, key=lambda s: s["total"])
print("Topper:", topper["name"])

import csv

with open("result.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["Name", "Total", "Percent", "Grade"])
    for s in students:
        writer.writerow([s["name"], s["total"], round(s["percent"], 2), s["grade"]])

print("Result saved to result.csv")