Python: skip comment lines marked with # in csv.DictReader

Another way to read a CSV file is using pandas

Here's a sample code:

df = pd.read_csv('test.csv',
                 sep=',',     # field separator
                 comment='#', # comment
                 index_col=0, # number or label of index column
                 skipinitialspace=True,
                 skip_blank_lines=True,
                 error_bad_lines=False,
                 warn_bad_lines=True
                 ).sort_index()
print(df)
df.fillna('no value', inplace=True) # replace NaN with 'no value'
print(df)

For this csv file:

a,b,c,d,e
1,,16,,55#,,65##77
8,77,77,,16#86,18#
#This is a comment
13,19,25,28,82

we will get this output:

       b   c     d   e
a                     
1    NaN  16   NaN  55
8   77.0  77   NaN  16
13  19.0  25  28.0  82
           b   c         d   e
a                             
1   no value  16  no value  55
8         77  77  no value  16
13        19  25        28  82

Good question. Python's CSV library lacks basic support for comments (not uncommon at the top of CSV files). While Dan Stowell's solution works for the specific case of the OP, it is limited in that # must appear as the first symbol. A more generic solution would be:

def decomment(csvfile):
    for row in csvfile:
        raw = row.split('#')[0].strip()
        if raw: yield raw

with open('dummy.csv') as csvfile:
    reader = csv.reader(decomment(csvfile))
    for row in reader:
        print(row)

As an example, the following dummy.csv file:

# comment
 # comment
a,b,c # comment
1,2,3
10,20,30
# comment

returns

['a', 'b', 'c']
['1', '2', '3']
['10', '20', '30']

Of course, this works just as well with csv.DictReader().

Actually this works nicely with filter:

import csv
fp = open('samples.csv')
rdr = csv.DictReader(filter(lambda row: row[0]!='#', fp))
for row in rdr:
    print(row)
fp.close()