Python - csv - Error: Sequence Expected

Question

I an attempting to use the python csv module to write a dictionary to a csv file.

My dictionary looks something like this:

{'PCIP': '192.168.1.4', 'DutIP': '192.168.1.6', 'timestamp': '20120410100340', 'start_time': '0.0', 
 'Transfer bytes': '59457090', 'Port': '5763', 'Lost Datagrams': '10575', 'Percent Lost Datagrams': 
 '20.727', 'PER': 20.727, 'Bandwidth bits': '51684334', 'Throughput': 51.684334, 'end_time': '9.2', 
 'Unknown': '41710', 'Jitter': '0.017', 'ID': '3', 'Total Datagrams': '51020'}

I get the error sequence expected when I attempt to write it.

Is there any way to do so?

def save_result_to_csv_file(self, file, data, header="", access_mode='ab'):
    """
    :param file: local file_name for csv-format logfile
    :type file: str
    :param data: a list or other datatype supported by csv.writerow() 
    :type data: list
    :param header: list containing row names
    :type header: list
    :param access_mode: 'a' append, 'w' write, 'ab' binary append, 'wb' binary write, 'r' read
    :type access_mode: str
    """
    #if file does not exist, start by writing the header row.

    log_file_obj = open(file, 'ab') 
    log_file_writer = csv.writer(log_file_obj)
    if not os.path.isfile(file):
        log_file_writer.writerow(header)
    log_file_writer.writerow(data)
    log_file_obj.flush()
    log_file_obj.close()

     # Labels (Compare to test_case_log_row definition, which matches row_labels)
    interval_data_labels = ["timestamp", "DutIP", "Port", "PCIP", "Unknown", "ID", "start_time", "end_time", "Transfer bytes", "Bandwidth bits"]
    summary_data_labels = interval_data_labels + ["Jitter", "Lost Datagrams", "Total Datagrams", "Percent Lost Datagrams"]
    timestamp_label = ["timestamp"]
    device_info_labels = [ "Device", "Device OS", "Device Bundle"]
    test_results_labels = ["Throughput (MBits/s)", "PER"]
    test_parameters_labels = ["pD.protocol", "pD.test_direction", "pD.execution_time", "pD.send_rate", "pD.packet_size", "pD.transfer_amount"]
    test_data_raw_labels = summary_data_labels
    row_labels = timestamp_label + device_info_labels + test_parameters_labels + test_results_labels + test_data_raw_labels

It is helpful to post the code that you've tried when asking a question like this. — Acorn
– Acorn, Commented Apr 10, 2012 at 14:13
As you're writing out a dictionary, have you specified the field names as header fields in the constructor? Only in that case can a dictionary be written out directly by csv.writerow() - if you don't set up header names (i.e., order of field names), writerow() will refuse to write dictionaries. — modelnine
– modelnine, Commented Apr 10, 2012 at 14:14
Yes, post the code, you have got the function arguments in the wrong order, I bet. — Ali Afshar
– Ali Afshar, Commented Apr 10, 2012 at 14:15
We mean you have to post the code where you are writing to the csv. My guess is you aren't using csv.DictWriter — Chris Wesseling
– Chris Wesseling, Commented Apr 10, 2012 at 14:18

Greg Leclercq · Accepted Answer · 2012-04-10 15:12:14Z

5

You could use the DictWriter object instead:

import csv

row = {'PCIP': '192.168.1.4', 'DutIP': '192.168.1.6', 'timestamp': '20120410100340', 'start_time': '0.0', 'Transfer bytes': '59457090', 'Port': '5763', 'Lost Datagrams': '10575', 'Percent Lost Datagrams': '20.727', 'PER': 20.727, 'Bandwidth bits': '51684334', 'Throughput': 51.684334, 'end_time': '9.2', 'Unknown': '41710', 'Jitter': '0.017', 'ID': '3', 'Total Datagrams': '51020'}

fp = open('/path/to/file', 'wb')
writer = csv.DictWriter(fp, fieldnames=row.keys())
writer.writerows([row])

Beware of the order of field names in row.keys().

answered Apr 10, 2012 at 15:12

Greg Leclercq

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Comments

Sergey Karpukhin · Accepted Answer · 2012-04-10 15:06:19Z

1

This snippet works ok in 2.7

import csv

my_dict =  {'PCIP': '192.168.1.4', 'DutIP': '192.168.1.6', 'timestamp': '20120410100340', 'start_time': '0.0', 
'Transfer bytes': '59457090', 'Port': '5763', 'Lost Datagrams': '10575', 'Percent Lost Datagrams': 
'20.727', 'PER': 20.727, 'Bandwidth bits': '51684334', 'Throughput': 51.684334, 'end_time': '9.2', 
'Unknown': '41710', 'Jitter': '0.017', 'ID': '3', 'Total Datagrams': '51020'}

writer = csv.writer(open("some.csv", "wb"))

writer.writerows(my_dict.viewitems())

If it is necessary to have keys in headers and columns to be the values one should use

writer.writerow(list(my_dict.viewkeys()))
writer.writerow(list(my_dict.viewvalues()))

edited Apr 10, 2012 at 15:06

answered Apr 10, 2012 at 14:28

Sergey Karpukhin

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6 Comments

Sergey Karpukhin Over a year ago

probably, you was using writerow() instead of writerows() - that caused 'sequence expected' error.

Parth Over a year ago

What does the csv file look like?

Parth Over a year ago

What I would like is the headers to be the keys and the columns to be the values. is that possible?

Parth Over a year ago

The headers appear correctly, but the fields appear like this: ('PCIP', '192.168.1.4') ('DutIP', '192.168.1.6') ('timestamp', '20120410113158')

Chris Wesseling Over a year ago

This won't work! Since in Python dicts have no order each time the OP calls save_result_to_csv_file, data might get written in a different order. As @Greg Leclercq's answer, and my comment on the question. Have a look at csv.DictWriter

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