title: Python count string (word) in column of a dataframe
body: <p>i have the following dataframe (df_hvl) with the columnname &quot;FzListe&quot; and the following data:</p>
  <pre><code>FzListe
  7MA1, 7OS1
  7MA1, 7ZJB
  7MA2, 7MA3, 7OS1
  76G1, 7MA1, 7OS1
  7MA1, 7OS1
  71E5, 71E6, 7MA1, FSS1
  71E4, 7MA1, 7MB1, 7OS1
  71E6, 7MA1, 7OS1
  7MA1
  7MA1, 7MB1, 7OS1
  7MA1
  7MA1, 7MA2, 7OS1
  04, 7MA1
  76G1, 7MA1, 7OS1
  76G1, 7MA1, 7OS1
  7MA1, 7OS1
  7MA1
  76G1, 7MA1, 7OS1
  76G1, 7MA1, 7OS1
  71E6, 7MA1
  7MA1, 7MA2, 7OS1
  7MA1
  7MA1
  7MA1
  7MA1, 7OS1
  76G1, 7MA1
  </code></pre>
  <p>I want to search for the string &quot;7MA&quot; only and count how often it appears in the list. (The list is originally much longer than that snippet). I want not to search only for 7MA1 because its possible that in one line it appears also with 7MA2 and/or 7MA3 and so on...</p>
  <p>The Dataframe is called df_hvl and i searched for a solution but didnt find one.</p>