# Session 1: Python Basics

## Contents

# Session 1: Python Basics#

## 1. Numbers#

## 1.1. Using Python as a calculator#

```
1 + 5
```

```
6
```

```
538687445 + 3897886465
```

```
4436573910
```

```
6 - 3
```

```
3
```

```
30 - 8
```

```
22
```

## 1.2. Variables#

The equals sign (“=”) means assignment, e.g., \(x = 1\) gives the value \(1\) to variable \(x\).

```
1 + 5
```

```
6
```

```
x = 1
y = 5
x + y
```

```
6
```

```
x = 3
x + y
```

```
8
```

```
z = x - y
z
```

```
-2
```

## Your turn:#

Create two variables: a and b. Assign 5 to a, and 10 to b

Calculate the sum of a and b, save it to a third variable called c

Calculate \(a \times b\) (hint: In Python, the multiplication sign is “*” [asterisk])

Calculate \(a \div b\) (The division sign is “/” [forward slash])

```
a = 5
b = 10
```

```
c = a + b
c
```

```
15
```

```
a * b
```

```
50
```

```
a / b
```

```
0.5
```

## Project#

Calculate \(1 + 2 +, ..., + k\)

Hint:

\[\frac{k \times (k + 1)}{2}\]

```
# step 1: determine k
k = 10
# step 2: write the equation
k * (k + 1) / 2
```

```
55.0
```

```
def calc_sum(k):
s = k * (k + 1) / 2
return s
```

```
calc_sum(k = 1_000_000)
```

```
500000500000.0
```

## 1.3 Strings#

```
s1 = "hello"
s2 = "Keen"
print(s1)
```

```
hello
```

```
print(s2)
```

```
Keen
```

```
print(s1 + s2)
```

```
helloKeen
```

```
print(s1 + ", " + s2)
```

```
hello, Keen
```

```
print(s1 + ", " + s2 + "!")
```

```
hello, Keen!
```

```
print("H" + s1[1:5] + ", " + s2 + "!")
```

```
Hello, Keen!
```

```
a = 2
b = 3
s = "Hi"
```

```
a + b
```

```
5
```

```
a1 = "4"
b5 = "14"
a1 + b5
```

```
'414'
```

## Project#

```
# tell me about you
name = "huijing"
age = 19
print("Hello, " + name + "! You are " + str(age) + " years old.")
```

```
Hello, huijing! You are 19 years old.
```

```
name
"H" + name[1:]
```

```
'Huijing'
```

## 1.4 Lists#

```
fruits = ["apple", "banana", "peach"]
keen = [2, 4, 1]
mom = [0, 1, 3]
```

```
# how many bananas did Keen eat this week?
print("Keen ate " + str(keen[1]) + " bananas this week.")
```

```
Keen ate 4 bananas this week.
```

```
# How many peaches did mon eat this week?
print("Mom ate " + str(mom[2]) + " peaches this week.")
```

```
Mom ate 3 peaches this week.
```

```
# How many bananas were eaten in total?
print("In total, " + str(keen[1] + mom[1]) + " were eaten this week")
```

```
In total, 5 were eaten this week
```