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

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