Populating a postgres table from a fixed width file using psycopg2 and pandas [duplicate]

I'm trying to read fixed width files and bulk load data to various tables on a postgres server. One file per one table of course.

I've wrote a function that creates the table for me already. I just need to populate it.

After some reading the docs and other research I've found two useful commands: "copy_from" within psycopg2 and ".to_sql" from pandas. I successfully created an implementation that uses the latter. The table looks great. The only issue is, it takes about 14 minutes to upload a file that is 110,000 rows and 100 columns.

The former approach is apparently a much faster method. I just cannot make it work yet.

Below is the code I have thus far:

import pandas as pd
import psycopg2 as pg

def sql_gen(cur,conn,filename,widths,col_names,table,header=False,chunk_size=10**5):

    df = pd.read_fwf(filename,widths=widths,index_col=False,header=None,iterator=True,
                     chunksize=chunk_size,names=cols)

    for chunk in df:
        cur.copy_from(df,table,null="")
        yield conn.commit()

#parameters
data_path = 'data.dat'
table = 'example_table'

#some stuff to extract stuff we need
widths = getwidths
cols = getcols

#main part of script
conn = None
try:
    conn = pg.connect('connectionstring')
    cursor = conn.cursor()

    for sql in sql_gen(cursor,conn,data_path,widths,cols,table):
        print(sql)

    # close communication with the PostgreSQL database server
    cursor.close()
except (Exception, pg.Error) as error :
    print(error)
finally:
    #closing database conn.
    if conn is not None:
        conn.close()
        print("PostgreSQL conn is closed")

I expected this to work but I am instead getting a TypeError:

argument 1 must have both .read() and .readline() methods

Full traceback as requested:

  File "<ipython-input-10-542d72b61dd4>", line 4, in <module>
    for sql in sql_gen(cursor,conn,data_path,widths,cols,table):

  File "<ipython-input-8-f82fb5831db3>", line 7, in sql_generator
    cur.copy_from(df,'example_table',null="")```