title: Python,Pandas, - How to search for an integer in a column
body: <p>This outwardly simple problem has been frustrating me for awhile.I am  new to python and  I can't get anywhere. I am looking to find a single integer in a specific one column of a large dataframe (600,000 records and 56 columns). Full match. I have recreated a simplified example here.</p>
  <p>eg How to find the number 5440499367 (2nd row) in this dataframe (epi) and return the results.</p>
  <pre><code>    KEY
  0   
  
  1   5440499367
  2   5040484761
  3   5404390876
  4   5444456006
  5   5040507739
  </code></pre>
  <pre><code>
  epi.info()
  
  &lt;class 'pandas.core.frame.DataFrame'&gt;
  RangeIndex: 6 entries, 0 to 5
  Data columns (total 1 columns):
   #   Column  Non-Null Count  Dtype
  ---  ------  --------------  -----
   0   KEY  6 non-null      int64
  dtypes: int64(1)
  memory usage: 176.0 bytes
  </code></pre>
  <p>Using</p>
  <pre><code>epi[&quot;KEY&quot;] == 5040501624
  0     True
  1    False
  2    False
  3    False
  4    False
  5    False
  Name: KEY, dtype: bool
  
  </code></pre>
  <p>so thats fine, I have created a boolean series which has found the number.
  When I try to do that in the large dataframe (I can't show that data because it has identifiers)</p>
  <p>eg below, I get an error and an empty row 0x56 columns.</p>
  <pre><code>found = df[df[&quot;KEY&quot;] == &quot;5440499367&quot;] 
  
  /opt/anaconda3/lib/python3.7/site-packages/pandas/core/computation/expressions.py:68: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
    return op(a, b)
  
  </code></pre>
  <p>I have tried also</p>
  <pre><code>5040501624 in epi[&quot;KEY&quot;]
  False
  
  </code></pre>
  <p>Which I feel is possibly the wrong use.
  I wondered if this was a datatype issue and have checked that the dtype is Int64 and in the 600,000 rows there are no empty values.</p>
  <p>What is the simplest way to do this ?</p>