ParserError: Too many columns in CSV (delimited file mismatch)

ParserError: Too many columns / Error tokenizing data

$ python - <<'PY'
import pandas as pd
from io import StringIO
pd.read_csv(StringIO('a,b\n1,2,3\n'))
PY
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
pandas.errors.ParserError: Error tokenizing data. C error: Expected 2 fields in line 2, saw 3

Why this happens

This ParserError typically occurs when the CSV (or any delimited text) file’s rows do not have the same number of columns as the header or expected number of fields. Common causes: wrong delimiter, stray delimiters inside quoted fields, inconsistent quoting, or broken lines.

Fix

Inspect the file for malformed lines or the wrong delimiter. Use sep to specify the correct delimiter, quoting to change how quotes are treated, or engine='python' for more permissive parsing. For broken data, skip corrupted lines (error_bad_lines=False in older pandas, on_bad_lines='warn'/'skip' in newer pandas).

Wrong code

import pandas as pd
# Data has 3 fields on row 2 but header has 2
pd.read_csv('file_with_bad_rows.csv')

Fixed code

import pandas as pd
from io import StringIO
data = 'a;b\n1;2;3\n'
# 1) Specify the proper delimiter
pd.read_csv(StringIO(data), sep=';')

# 2) Skip problematic lines (use with caution)
pd.read_csv(StringIO('a,b\n1,2,3\n'), on_bad_lines='skip')

# 3) Use the python engine for complex quoting
pd.read_csv(StringIO('a,b\n"1,2",3\n'), engine='python')