str()

str(x) converts x into a string, where x can be any value.

1
x = 123
2
y = str(x)
3
print(y) #"123"
4
print(type(y)) #<class 'str'>

Note

type(y) returns the type of the variable y.

If we invoke the str function without providing an argument, it will return an empty string.

Note

We may visit this in a later chapter, but str returns the __str__ method of the object if it exists, otherwise it returns the __repr__ method.

bool()

bool(x) returns False if x is falsy, otherwise it returns True. By default everything is considered truthy, except for:

• Constants defined to be false: None, False,
• Zero numeric values: 0, 0.0, 0j
• Empty sequences and collections: '', (), [], {}, set(), range(0)

1
print(bool(0)) #False
2
print(bool(1)) #True
3
print(bool("")) #False
4
print(bool("Hello")) #True

If we invoke the bool function without providing an argument, it will return False.

1
print(bool()) #False

int()

int(x) converts x into an integer, where x can be any value.

• For floating point numbers, this truncates towards zero.
• If x is a string, then this literal can be preceded by + or - and be surrounded by whitespace (this string should represent an integer). For example: int("+123") will return 123, int("-123") will return -123, int("123 ") will return 123. We can also provide a second argument, which is the base of the number system to convert to. For example: int("123", 8) will return 83 because 123 in base 8 is 83.
• If x is a Boolean, then it returns 1 if it’s True, otherwise 0.

We can’t convert complex numbers to integers.

1
print(int(123.45)) #123
2
print(int("-123")) #-123
3
print(int("-1_234")) #-1234
4
print(int("   -123   ")) #-123
5
print(int("123", 8)) #83
6
print(int(True)) #1
7
print(int(False)) #0
8
print(int(2+3j)) #TypeError: can't convert complex to int

float()

float(x) converts x into a floating point number, where x can be any value.

• For integers, this converts the integer to a floating point number.
• If x is a string, then this literal can be preceded by + or - and be surrounded by whitespace (this string should represent a floating point number). For example: float("+123.45") will return 123.45, float("-123.45") will return -123.45, float("123.45 ") will return 123.45. The argument may also represent NaN, Infinity or -Infinity.
• If x is a Boolean, then it returns 1.0 if it’s True, otherwise 0.0.

We can’t convert complex numbers to floating point numbers.

1
print(float(123)) #123.0
2
print(float("-123.45")) #-123.45
3
print(float("123.45 ")) #123.45
4
print(float("123_456.7_891_234 ")) #123456.7891234
5
print(float("NaN")) #nan
6
print(float("Infinity")) #inf
7
print(float("-Infinity")) #-inf
8
print(float(True)) #1.0
9
print(float(False)) #0.0
10
print(float(2+3j)) #TypeError: can't convert complex to float

complex()

complex(x) converts x into a complex number, where x can be any value.

• For integers and floating point numbers, this converts the number to a complex number with imaginary part 0.
• If x is a string, then this string should represent a valid complex number Op1xOp2yj where both Op1 and Op2 can be +, or - (for the Op1 it can be nothing), and optionally surrounded by whitespace. For example: complex("2+3j") will return 2+3j, complex("3j") will return 3j, complex(" 123.45+67.89j") will return 123.45+67.89j. As both numbers are float, each one could also represent NaN, Infinity or -Infinity. Lastly the complex number could be surrounded by brackets.
• If x is a Boolean, then it returns 1.0 if it’s True, otherwise 0.0.
• The last variation allows us to provide two arguments, the first one is the real part, and the second one is the imaginary part.

1
print(complex(123)) #(123+0j)
2
print(complex(-123.45)) #(-123.45+0j)
3
print(complex(False)) #(0+0j)
4
print(complex("123.45")) #(123.45+0j)
5
print(complex("123.45+67.89j")) #(123.45+67.89j)
6
print(complex("    123.45-67.89j   ")) #(123.45-67.89j)
7
print(complex("(123.45+67.89j)")) #(123.45+67.89j)
8
print(complex(123, 456)) #(123+456j)

type()

type(x) returns the type of the variable x.

1
print(type(123)) #<class 'int'>
2
print(type(123.45)) #<class 'float'>
3
print(type(123.45+67.89j)) #<class 'complex'>
4
print(type(True)) #<class 'bool'>
5
print(type("123")) #<class 'str'>

Exercises

1
x = input("Enter a number: ")
2
y = input("Enter another number: ")
3
z = x + y
4
print(z)

1
x = int(input("Enter a number: "))
2
y = int(input("Enter another number: "))
3
z = x + y
4
print(z)

1
x = "1"
2
y = "234"
3
z = "56.78"
4
t = int(x) + int(y) + int(z)
5
print(t)

1
x = "1"
2
y = "234"
3
z = "56.78"
4
t = int(x) + int(y) + int(float(z)) # Convert it to float first, then to an integer
5
print(t)

1
Please enter the first number: 10
2
Please enter the second number: 20
3
The sum of the two numbers is 30

1
x = int(input("Please enter the first number: "))
2
y = int(input("Please enter the second number: "))
3
z = x + y
4
print("The sum of the two numbers is", z)

1
Please enter the temperature in Celsius: 20
2
The temperature in Fahrenheit is 68

1
temp = float(input("Please enter the temperature in Celsius: "))
2
fahrenheit = (temp * 9/5) + 32
3
print("The temperature in Fahrenheit is", fahrenheit)