Python: Pandas filter string data based on its string length

Question

I like to filter out data whose string length is not equal to 10.

If I try to filter out any row whose column A's or B's string length is not equal to 10, I tried this.

df=pd.read_csv('filex.csv')
df.A=df.A.apply(lambda x: x if len(x)== 10 else np.nan)
df.B=df.B.apply(lambda x: x if len(x)== 10 else np.nan)
df=df.dropna(subset=['A','B'], how='any')

This works slow, but is working.

However, it sometimes produce error when the data in A is not a string but a number (interpreted as a number when read_csv read the input file).

  File "<stdin>", line 1, in <lambda>
TypeError: object of type 'float' has no len()

I believe there should be more efficient and elegant code instead of this.

---

Based on the answers and comments below, the simplest solution I found are:

df=df[df.A.apply(lambda x: len(str(x))==10]
df=df[df.B.apply(lambda x: len(str(x))==10]

or

df=df[(df.A.apply(lambda x: len(str(x))==10) & (df.B.apply(lambda x: len(str(x))==10)]

or

df=df[(df.A.astype(str).str.len()==10) & (df.B.astype(str).str.len()==10)]

Answer 1

import pandas as pd

df = pd.read_csv('filex.csv')
df['A'] = df['A'].astype('str')
df['B'] = df['B'].astype('str')
mask = (df['A'].str.len() == 10) & (df['B'].str.len() == 10)
df = df.loc[mask]
print(df)

Applied to filex.csv:

A,B
123,abc
1234,abcd
1234567890,abcdefghij

the code above prints

            A           B
2  1234567890  abcdefghij