if statement: whether an array has units/dimensions (pint)

My variable C0 is defined in pint.UnitRegistry units mol/L. I need to use it in a function, but in order for Python to not call me on inconsistent units for the general function, I have to define a new variable in the function with units, as follows.

import pint
u = pint.UnitRegistry()

C0      = [10**(-3),10**(-6),0] *u.mol/u.L

def r(c,t):
    C = c * u.mol/u.L   #Python expects c to be dimensionless
    return ν * k[3]*C0[1]*C[0] / ((k[2]+k[3])/k[1] + C[0]) #k and ν are arrays for the problem I'm working on.

I want to add an if statement so that I don't end up with C in r(C0,t) being in units of mol^2/L^2. What I have is

def r(c,t):
    if c.dimensionless == True:
        C = c * u.mol/u.L
    else:
        C = c
    return ν * k[3]*C0[1]*C[0] / ((k[2]+k[3])/k[1] + C[0])

But when I run this with C0, it tells me that C0 has no attribute called dimensionless. How should I edit my if statement so it will work to check any kind of input for units?

Traceback:

File [Redacted], line 32, in <module>
    Ct = odeint(r,C0,t)

  File "C:\Users\Spencer\Anaconda3\lib\site-packages\scipy\integrate\odepack.py", line 233, in odeint
    int(bool(tfirst)))

  File [Redacted], line 24, in r
    if c.dimensionless == True:

AttributeError: 'numpy.ndarray' object has no attribute 'dimensionless'```