title: Using assign and lambda to combine year and month columns into 1 date column
body: <p>I have an Excel file with the following columns that I read into a pandas dataframe:</p>
  
  <pre><code>Year    Month   Day   Hour
  2012    1       1     0
  2012    1       1     1
  2012    1       1     2
  2012    1       1     3`
  </code></pre>
  
  <p>I'm trying to combine these 3 columns into a datetime column using the following code:</p>
  
  <pre><code>df1 = df.assign(Dt = lambda row: datetime.datetime(row['Year'].astype(int), row['Month'].astype(int)...))
  </code></pre>
  
  <p>This code gives the following error: 
     <code>Type Error: Cannot convert the series to (Type 'int')</code></p>
  
  <p>I know I can just combine these columns into a string and use <code>strptime</code> to convert to <code>datetime</code>. HoweverI i want to try to understand what i'm doing wrong with assign and lambda here.</p>