I create a list of more than a thousand file (Basically now I have a list with the name of the file) now in order to make the man I thought to do something like this (suppose asch file have 20 lines):

matrix = np.zeros((len(file_list),10))

then I'm going to charge the matrix .. with something like :

for i,j in zip(len(file_list)) :matrix[i].append(np.genfromtxt('name1',usecols=(1,))) 

Now is there a way not to define the number of file's line ???

then .. how can i make a mean between this file ??

Ops I see that numpy array have not append ..how can I do

First, you can just store them in a list:

My_list = []
for i,j in zip(len(file_list)) :My_list.append(np.genfromtxt('name1',usecols=(1,)))  

Assuming that all your files have the same number of lines and columns, you can then convert it to a numpy array:

My_list = np.array(My_list)

My_list is now a numpy array, with dimensions corresponding to the size of the loaded files + one corresponding to the number of files.

Note that I did not check the way you're loading files.