I'm reading in large csv files into pandas some of them with String columns in the thousands of characters. Is there any quick way to limit the width of a column, i.e. only keep the first 100 characters?

If you can read the whole thing into memory, you can use the str method for vector operations:

>>> df = pd.read_csv("toolong.csv")
>>> dfa                       b  c
0  1  1256378916212378918293  2[1 rows x 3 columns]
>>> df["b"] = df["b"].str[:10]
>>> dfa           b  c
0  1  1256378916  2[1 rows x 3 columns]

Also note that you can get a Series with lengths using

>>> df["b"].str.len()
0    10
Name: b, dtype: int64

I was originally wondering if

>>> pd.read_csv("toolong.csv", converters={"b": lambda x: x[:5]})a      b  c
0  1  12563  2[1 rows x 3 columns]

would be better but I don't actually know if the converters are called row-by-row or after the fact on the whole column.