ValueError: could not convert string to float

ValueError: could not convert string to float: ‘abc’

$ python -c "import pandas as pd; df = pd.DataFrame({'a':['1.2','two','3.4']}); df['a'].astype(float)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ValueError: could not convert string to float: 'two'

Why this happens

A ValueError: could not convert string to float means at least one value in the column cannot be parsed as a numeric value. Common causes: non-numeric text, thousands separators (commas), stray characters, or localized decimal separators.

Fix

Use pd.to_numeric(..., errors='coerce') to convert invalid values to NaN, clean the strings (str.replace to remove commas), or use locale-aware parsing if necessary.

Wrong code

import pandas as pd

df = pd.DataFrame({'a': ['1.2', 'two', '3.4']})
# raises ValueError
print(df['a'].astype(float))

Fixed code

import pandas as pd

# Convert safely by coercing errors to NaN
df['num'] = pd.to_numeric(df['a'], errors='coerce')
print(df['num'])

# Or clean strings first (remove thousands separators etc.)
df['clean'] = df['a'].str.replace(',', '').astype(float)
print(df['clean'])