How to convert a string to a complex number in Python?

Question

I'm trying to convert an input string to a float but when I do it I keep getting some kind of error, as shown in the sample below.

>>> a = "3 + 3j"
>>> b = complex(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: complex() arg is a malformed string

Solution 1

From the documentation:

Note

When converting from a string, the string must not contain whitespace around the central + or - operator. For example, complex('1+2j') is fine, but complex('1 + 2j') raises ValueError.

Solution 2

Following the answer from Francisco Couzo, the documentation states that

When converting from a string, the string must not contain whitespace around the central + or - operator. For example, complex('1+2j') is fine, but complex('1 + 2j') raises ValueError.

Remove all the spaces from the string and you'll get it done, this code works for me:

a = "3 + 3j"
a = a.replace(" ", "") # will do nothing if unneeded
b = complex(a)

Solution 3

complex's constructor rejects embedded whitespace. Remove it, and it will work just fine:

>>> complex(''.join(a.split()))  # Remove all whitespace first
(3+3j)

Comments

[Tyberius]

Eval you have to careful once you move to the case of parsing text from user input or a file rather than just entering your own complex number as a string.