Python histogram of split() data

I am trying to make a histgramm over a text file containing floats:

import matplotlib.pyplot as plt

c1_file = open('densEst1.txt','r')
c1_data =  c1_file.read().split()    
c1_sum = float(c1_data.__len__())

plt.hist(c1_data)
plt.show()

The output of c1_data.__len__() works fine, but hist() throws:

C:\Python27\python.exe "C:/x.py"
Traceback (most recent call last):
  File "C:/x.py", line 7, in <module>
    plt.hist(c1_data)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 2958, in hist
    stacked=stacked, data=data, **kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\__init__.py", line 1812, in inner
    return func(ax, *args, **kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes\_axes.py", line 5995, in hist
    if len(xi) > 0:
TypeError: len() of unsized object