How to add a specific number of characters to the end of string in Pandas?

Question

I am using the Pandas library within Python and I am trying to increase the length of a column with text in it to all be the same length. I am trying to do this by adding a specific character (this will be white space normally, in this example I will use "_") a number of times until it reaches the maximum length of that column.

For example:

Col1_Before

A
B
A1R
B2
AABB4

Col1_After

A____
B____
A1R__
B2___
AABB4

So far I have got this far (using the above table as the example). It is the next part (and the part that does it that I am stuck on).

df['Col1_Max'] = df.Col1.map(lambda x: len(x)).max()
df['Col1_Len'] = df.Col1.map(lambda x: len(x))
df['Difference_Len'] = df ['Col1_Max'] - df ['Col1_Len']

I may have not explained myself well as I am still learning. If this is confusing let me know and I will clarify.

Answer 1

Without creating extra columns:

In [63]: data
Out[63]: 
    Col1
0      A
1      B
2    A1R
3     B2
4  AABB4

In [64]: max_length = data.Col1.map(len).max()

In [65]: data.Col1 = data.Col1.apply(lambda x: x + '_'*(max_length - len(x)))

In [66]: data
Out[66]: 
    Col1
0  A____
1  B____
2  A1R__
3  B2___
4  AABB4