Argument 1 must be string, not datetime.datetime?
<p>I just took a Data Analysis course on Udacity.
My code is:</p>

<pre><code>enrollments_filename= '/Users/abc/Desktop/Udacity - Intro to Data Analysis/enrollments.csv'

def open_file(filename):
    with open(filename, 'rb') as f:
        reader = unicodecsv.DictReader(f)
        return list(reader)

enrollments = open_file(enrollments_filename)

# Takes a date as a string, and returns a Python datetime object. 
# If there is no date given, returns None

from datetime import datetime as dt    
def parse_date(date):
    if date == '':
        return None
    else:
        return dt.strptime(date, '%Y-%m-%d')

# Takes a string which is either an empty string or represents an integer,
# and returns an int or None.

def parse_maybe_int(i):
    if i == '':
        return None
    else:
        return int(i)

for enrollment in enrollments:
    enrollment['cancel_date'] = parse_date(enrollment['cancel_date'])
    enrollment['days_to_cancel'] = parse_maybe_int(enrollment['days_to_cancel'])
    enrollment['is_canceled'] = enrollment['is_canceled'] == 'True'
    enrollment['is_udacity'] = enrollment['is_udacity'] == 'True'
    enrollment['join_date'] = parse_date(enrollment['join_date'])

enrollments[0]    
</code></pre>

<p>Here is the error I got:</p>

<pre><code>TypeError: strptime() argument 1 must be string, not datetime.datetime
</code></pre>

<p>Can anyone explain to me why? When I change <code>date</code> to <code>str(date)</code>, here is the error I got:</p>

<pre><code>//anaconda/lib/python2.7/_strptime.pyc in _strptime(data_string, format)
    333     if len(data_string) != found.end():
    334         raise ValueError("unconverted data remains: %s" %
--&gt; 335                           data_string[found.end():])
    336 
    337     year = None


ValueError: unconverted data remains:  00:00:00
</code></pre>

<p>The weird thing is, when I first ran the code, it works. But then I re-pressed the second time and it returned the error! Thanks very much!</p>

<p>I bet you ran this line twice in your shell/session:</p>

<pre><code>enrollment['cancel_date'] = parse_date(enrollment['cancel_date'])
</code></pre>

<p>The first time works, but now enrollment['cancel_date'] is a date, not a string. Second time you ran it - error.</p>

python datetime