Python: convert string-pair to complex number

Question

Here is my complex number. *I retrieved it out of a file:

re, im = line[11:13]
print(re) # -4.04780617E-02
print(im) # +4.09889424E-02

At the moment, it is just a pair of strings. How can I combine these into a complex number?

I've tried five times:

z = complex(re, im)
# ^ TypeError: complex() can't take second arg if first is a string

z = complex(float(re), float(im))
# ^ ValueError: could not convert string to float: re(tot)

z = float(re) + float(im) * 1j
# ^ ValueError: could not convert string to float: re(tot)

z = complex("(" + re + im + "j)")
# ValueError: complex() arg is a malformed string

z_str = "(%s%si)" % (re, im) # (-4.04780617E-02+4.09889424E-02i)
z = complex(z_str)
# ValueError: complex() arg is a malformed string

what do you mean by combine? what are you trying to achieve? I see two real numbers. One positive and another negative. How do you want them to combine to a complex number? — Bibhas Debnath
– Bibhas Debnath, Commented Jan 21, 2014 at 14:02

Ivo van der Wijk · Accepted Answer · 2014-01-21 14:05:32Z

5

Python uses 'j' as suffix for the imaginary part:

>>> complex("-4.04780617E-02+4.09889424E-02j")
(-0.0404780617+0.0409889424j)

In your case,

z_str = "(%s%sj)" % (re, im) # (-4.04780617E-02+4.09889424E-02i)
z = complex( z_str )

answered Jan 21, 2014 at 14:05

Ivo van der Wijk

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P i Over a year ago

Note to self: Mathematicians say i, engineers say j. Computer code is engineering :)

b3orn · Accepted Answer · 2014-01-21 14:08:27Z

2

z = complex(float(re), float(im))

answered Jan 21, 2014 at 14:08

b3orn

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P i Over a year ago

Thanks -- this is the simplest way! Due to an error elsewhere in my code, I was getting garbage values for re, im.

djokester · Accepted Answer · 2016-06-28 12:41:54Z

0

To convert a string into a complex number all you need to do is

c = complex(str)

Where str is a string of form "a+bj" or "a*bj" like "-5-3j"

However if you have the real and imaginary parts separately as string pairs. You can do the following

c = complex(float(re),float(im))

answered Jun 28, 2016 at 12:41

djokester

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