Sort dataframe by string length

You can use reindex of index of Series created by len with sort_values:

print (df.name.str.len())
0    5
1    2
2    6
3    4
Name: name, dtype: int64

print (df.name.str.len().sort_values())
1    2
3    4
0    5
2    6
Name: name, dtype: int64

s = df.name.str.len().sort_values().index
print (s)
Int64Index([1, 3, 0, 2], dtype="int64")

print (df.reindex(s))
     name  score
1      Al      4
3    Greg      3
0   Steve      2
2  Markus      2

df1 = df.reindex(s)
df1 = df1.reset_index(drop=True)
print (df1)
     name  score
0      Al      4
1    Greg      3
2   Steve      2
3  Markus      2