If statement with negative condition

I want to prepare my data for a histogram. My data (in the following code described with D) contains values between [-200,1000] and with an if statement I want to allocate them to bins of the range [0,20]. My code looks like this:

for t in range(0,731):
     if(D[t]<(-130)):
        xbin[t]=0
     if(D[t]>=(-130) and D[t]<=(-120)):
        xbin[t]=1
     if(D[t]>=(-120) and D[t]<=(-110)):
        xbin[t]=2
     if(D[t]>=(-110) and D[t]<=(-100)):
        xbin[t]=3
     if(D[t]>=(-100) and D[t]<=(-50)):
        xbin[t]=4
     if(D[t]>=(-50) and D[t]<=0):
        xbin[t]=5
     if(D[t]>=0 and D[t]<=50):
        xbin[t]=6

and so on. But it seems as the program does not understand the negative condition in the if statement. So it allocate all values <0 to xbin=6 doesn't matter if the value is < -120, < -130 or something else. How can I fix this? Thank you!