Today I've also posted a question to scipy groups because I've thought I've found a solution but this work good bar(N, b1[:,0], width, color='r', yerr=binterv) ############ s3=find(sig1[:,arange(ini,c)]<=0.001) b1=b.flatten() #if s3!=[]: for i3 in arange(len(s3)): text(s3[i3], b1[s3[i3]+ini],'***') s2=find(logical_and(sig1[:,arange(ini,c)]>0.001,sig1[:,arange(ini,c)]<=0.01)) for i2 in arange(len(s2)): text(s2[i2], b1[s2[i2]+ini],'**') s1=find(logical_and(sig1[:,arange(ini,c)]>0.01,sig1[:,arange(ini,c)]<=0.05)) for i1 in arange(len(s1)): text(s1[i1], b1[s1[i1]+ini],'*') title('Plot of the coefficients of the model') and when i uncomment the ifs3!=[] part it does not... so in this case I've solve the problem.. but is there an equivalent for isempty matlab command in numpy ? Thanks in advance for the reply Giorgio