title: time data doesn't match format specified when it seemed to be match
body: <p>I have dataframe in pandas that has two dates columns:</p>
  <pre><code>&gt;&gt;&gt;ID  name    start        end  
  0  12  Tik     1/6/2020    None
  1  32  Tak     12/31/2019  None
  2  45  Tek     9/1/2019   1/30/2020
  3  78  Tok     9/1/2019   1/29/2020
  </code></pre>
  <p>I'm trying to convert those dates into datetime to be in format of Y-m-d e.g that 12/31/2019 will be 2019-12-31 :</p>
  <pre><code>df[['start','end']] =df[['start','end']].apply(pd.to_datetime, format=''%Y-%m-%d'')
  
  </code></pre>
  <p>but whenever I run this I get error:</p>
  <blockquote>
  <p>ValueError: time data 1/6/2020 doesn't match format specified</p>
  </blockquote>
  <p>I have tried than to specify the format to be like the given date (e.g (d-m-Y):</p>
  <pre><code>df[['start','end']] =df[['start','end']].apply(pd.to_datetime, format=''%d-%m-%Y'')
  
  &gt;&gt;&gt;ValueError: time data '1/6/2020' does not match format '%d-%m-%Y' (match)
  </code></pre>
  <p>I have tried to break it as suggest in the first answer here: <a href="https://stackoverflow.com/questions/38067704/how-to-change-the-datetime-format-in-pandas">How to change the datetime format in pandas</a>
  and to first conver to  datetime and then use strftime but in the first line I got the error that Ineed to specify the format.</p>
  <p>I can't find any reason why is this happen, maybe is because the day and month do not have two digits?</p>
  <p>my end goal is to convert those date columns into %Y-%m-%d format</p>