Python Type Conversion

What Is Type Conversion in Python?

Type conversion means changing one type of data into another type.

That’s it. Simple idea.

Like changing a shirt. Same person. Different clothes.

We have a value. We change its type. The value stays the same. But the type changes.

Why Do We Need Type Conversion?

Good question. Let me give us a real example.

Imagine we ask the user for their age.

age = input("Enter your age: ")

The user types 25.

But here is the problem. input() always gives us a string. Always. Even if the user types a number.

So age is not 25 (a number). It is "25" (a string).

Now if we try to do math with it:

next_year_age = age + 1

We will get an error. Because we cannot add a string and a number.

print("25" + 1)   # Error!

We need to convert age from a string to a number first.

age = int(input("Enter your age: "))
next_year_age = age + 1
print(next_year_age)

Now it works. Because age is a number, not a string.

That is why we need type conversion. To change data from one type to another when we need it.

The Main Type Conversion Functions in Python

Python has built-in functions for converting between types.

Let me show us each one.

Converting to Integer — int()

int() converts something to an integer.

From float to int:

x = 3.7
y = int(x)
print(y)

3

Wait. Why 3? Why not 4?

Because int() does not round. It just chops off the decimal part. Always.

print(int(3.1))    # 3
print(int(3.9))    # 3
print(int(-3.7))   # -3

It does not round. It just removes the decimal. Let’s remember that.

If we want to round, we use round() instead.

print(round(3.7))   # 4
print(round(3.1))   # 3

From string to int:

x = "25"
y = int(x)
print(y)

25

Now y is a number. We can do math with it.

print(y + 5)   # 30

But careful. The string must contain a valid number.

x = "hello"
y = int(x)    # Error!

ValueError: invalid literal for int() with base 10: 'hello'

We cannot convert “hello” to a number. It does not make sense.

But this works:

x = "25"
y = int(x)    # Works

And this also works:

x = " 25 "
y = int(x)    # Works, spaces are ignored

From boolean to int:

print(int(True))    # 1
print(int(False))   # 0

Because True is 1 and False is 0.

Converting to Float — float()

float() converts something to a float (decimal number).

From int to float:

x = 25
y = float(x)
print(y)

25.0

From string to float:

x = "3.14"
y = float(x)
print(y)

3.14

x = "25"
y = float(x)
print(y)

25.0

Even “25” becomes 25.0. Because floats always have a decimal point.

From boolean to float:

print(float(True))    # 1.0
print(float(False))   # 0.0

Converting to String — str()

str() converts something to a string.

From int to string:

x = 25
y = str(x)
print(y)

25

But wait. It looks the same. How do we know it changed?

Check the type:

print(type(x))   # <class 'int'>
print(type(y))   # <class 'str'>

See? Different types. Even though they look the same when printed.

From float to string:

x = 3.14
y = str(x)
print(y)
print(type(y))

3.14
<class 'str'>

From boolean to string:

x = True
y = str(x)
print(y)
print(type(y))

True
<class 'str'>

Notice — True becomes "True". It looks the same. But it is now a string, not a boolean.

Why Converting to String Is Useful

Here is a common situation.

We have a number. We want to add it to a message.

age = 25
message = "I am " + age + " years old"

This gives an error. Because we cannot add a string and a number.

So what do we do? We convert the number to a string.

age = 25
message = "I am " + str(age) + " years old"
print(message)

I am 25 years old

That works.

But there is a better way. We will learn about f-strings in a later tutorial. They make this much easier.

Converting to Boolean — bool()

bool() converts something to a boolean.

We learned about this in the last tutorial. But let me remind us.

print(bool(1))       # True
print(bool(0))       # False
print(bool(5))       # True
print(bool(0.0))     # False
print(bool("hello")) # True
print(bool(""))      # False

The rule is simple:

• Falsy values become False
• Everything else becomes True

Falsy values are: False, None, 0, 0.0, "", empty collections.

Everything else is truthy. And becomes True.

Python Type Conversion: A Real-Life Example

Let’s build a simple calculator.

num1 = input("Enter first number: ")
num2 = input("Enter second number: ")

sum = num1 + num2
print("The sum is:", sum)

What happens if we run this?

If we enter 5 and 3, the output is:

The sum is: 53

Wait. That is wrong. It should be 8.

Why did it give 53?

Because input() gives strings. So num1 is "5" and num2 is "3". And "5" + "3" gives "53". String concatenation, not addition.

To fix this, we need to convert them to numbers.

num1 = input("Enter first number: ")
num2 = input("Enter second number: ")

num1 = int(num1)
num2 = int(num2)

sum = num1 + num2
print("The sum is:", sum)

Now if we enter 5 and 3, the output is:

The sum is: 8

Because now num1 is 5 (a number) and num2 is 3 (a number). And 5 + 3 is 8.

That is why type conversion matters. It changes how the data behaves.

Common Mistakes with Python Type Conversion

x = "25.5"
y = int(x)

ValueError: invalid literal for int() with base 10: '25.5'

x = "25.5"
y = float(x)
print(y)

25.5

x = "25.5"
y = int(float(x))
print(y)

25

x = 3.9
y = int(x)
print(y)   # 3, not 4

print(round(3.9))   # 4

x = "hello"
y = int(x)   # Error!

Checking the Type in Python

We can always check the type of a value using type().

x = 25
print(type(x))       # <class 'int'>

y = str(x)
print(type(y))       # <class 'str'>

z = float(x)
print(type(z))       # <class 'float'>

This is useful when we are not sure what type something is.

Summary of Python Type Conversions

Let me show us a table.

Next, we will learn about Getting User Input so we can continue step by step.