Need to remove duplicates for a list with in a function
<p>this is what i have so far:</p>

<pre><code>def unique_element(group):
  list=[]
  for element in group:
      piece=parse_formula(element)
      for x in piece:
          list.append(x[0])


  return list #list(set(list)) 
</code></pre>

<p>I have the other function below but this is the one I am trying to fix. Right now it returns a function with a list of letters but I do not want repeating letters. Example:</p>

<pre><code>unique_element(['H2O2Y2','R3O2','Y2S3'])
['H', 'O', 'Y', 'R', 'O', 'Y', 'S']
</code></pre>

<p>I thought using <code>list(set(list))</code> would work but when i run the function i get:</p>

<pre><code>unique_element(['H2O2Y2','R3O2','Y2S3'])
</code></pre>

<p>Traceback (most recent call last):</p>

<pre><code>File "&lt;stdin&gt;", line 1, in &lt;module&gt;
File "_sage_input_61.py", line 10, in &lt;module&gt;
  exec compile(u'print _support_.syseval(python, u"unique_element([\'H2O2Y2\',\'R3O2\',\'Y2S3\'])", __SAGE_TMP_DIR__)
File "", line 1, in &lt;module&gt;

File "/sagenb/sage_install/sage-5.4-sage.math.washington.edu-x86_64-Linux/devel/sagenb-git/sagenb/misc/support.py", line 479, in syseval
  return system.eval(cmd, sage_globals, locals = sage_globals)
File "/sagenb/sage_install/sage-5.4-sage.math.washington.edu-x86_64-Linux/local/lib/python2.7/site-packages/sage/misc/python.py", line 56, in eval
    eval(z, globals)
File "", line 1, in &lt;module&gt;

File "", line 10, in unique_element

TypeError: 'list' object is not callable
</code></pre>

<p>other functions:</p>

<pre><code>    from numpy import *
    from scipy import *
    from pylab import *
    import re
def parse_formula(formula):
'''Given a simple chemical formula, return a list of (element, multiplicity) tuples.

Example:
'H2SO4' --&gt; [('H', 2.0), ('S', 1.0), ('O', 4.0)]


'''

return [ (elem, float(mul) if mul else 1.) for (elem, mul) in re.findall(r'([A-Z][a-z]*)(\d*)', formula) ]
</code></pre>
