Python complex()

Python complex() function takes real, imaginary numbers and strings as input and converts them into a complex number. This method takes two optional parameters (real and imaginary) and returns a complex number as output.

complex() Syntax 

The syntax of complex() is:

complex([real[, imaginary]])

complex() Parameters

The complex() method can take two parameters, and both are optional.

• real (optional) – A number representing the real part of the complex number. The real number can be of a string like ‘3+5j‘. If not set anything, it defaults to 0.
• imaginary (optional) – A number representing the imaginary part of the complex number. If not set anything, it defaults to 0.

If the first parameter is passed as a string, then it will be interpreted as a complex number. In this case, the second parameter should be omitted.

complex() Return Value

It returns the complex number as output. 

Note: In string conversion, it must not contain whitespace around the operator (+ or -). Example – complex('1+2j') is fine, but complex('1 + 2j') raises ValueError.

Example 1: How to create a complex number in Python?

In this example, we will take a look at creating the complex number using real numbers with integer, float and string. 

# Code to illustrate complex number

# covert real number to complex
num = complex(5,3)
print(num)

# covert real number to complex
num = complex(5,-4)
print(num)

# Default if no parameter is passed to complex method
num = complex()
print(num)

# In case if you pass only real number, defaults imaginary to 0
num = complex(5)
print(num)

# In case if you pass only real number, defaults imaginary to 0
num = complex(-2)
print(num)

# In case if you pass only float number, defaults imaginary to 0
num = complex(5.6,4)
print(num)

# if string is passed, it will be interpreted as complex number
num = complex('8')
print(num)

# if string is passed, it will be interpreted as complex number
num = complex('1+2j')
print(num)

Output

(5+3j)
(5-4j)
0j
(5+0j)
(-2+0j)
(5.6+4j)
(8+0j)
(1+2j)

Example 2: TypeError while converting string with imaginary parameter

If the first parameter is passed as a string, then it will be interpreted as a complex number. In this case, the second parameter should be omitted. Otherwise, you get the TypeError: complex() can’t take second arg if first is a string

# Code to illustrate complex number

# if string is passed with imaginary number
num = complex('8',5)
print(num)

Output

Traceback (most recent call last):
  File "c:\Projects\Tryouts\listindexerror.py", line 4, in <module>
    num = complex('8',5)
TypeError: complex() can't take second arg if first is a string

Example 3: ValueError if string operator has a space 

In the case of string conversion, if there is any space around the operator, Python will raise ValueError: complex() arg is a malformed string

# if you give a space in the string
num = complex('1 + 2j')
print(num)

Output

Traceback (most recent call last):
  File "c:\Projects\Tryouts\listindexerror.py", line 4, in <module>
    num = complex('1 + 2j')
ValueError: complex() arg is a malformed string