Casting

Casting means changing a value from one type to another. Python offers the constructors int(), float(), and str().

int()

Builds an integer from an int, a float (truncating), or a string:

python
x = int(1)

### 1
y = int(2.8)

### 2
z = int("3")

### 3

A string like "3.8" fails with int():

python
int("3.8")

### ValueError: invalid literal

float()

Builds a float from an int, a float, or a numeric string:

python
x = float(1)

### 1.0
y = float(2.8)

### 2.8
z = float("3")

### 3.0
w = float("4.2")

### 4.2

str()

Builds a string from almost anything:

python
x = str("s1")

### 's1'
y = str(2)

### '2'
z = str(3.0)

### '3.0'

Why cast?

The most common reason is printing a number next to text:

python
age = 36
print("I am " + str(age) + " years old.")

Without str(), adding a string and an int raises a TypeError.

TL;DR

• int(value) makes an integer (truncates floats).
• float(value) makes a float.
• str(value) makes a string.
• Cast to str before gluing numbers into text.