How do I fill a column with one value in Pandas?

Question

I have a column with consecutive digits in a Pandas DataFrame.

A
1
2
3
4

I would like to change all those values to a simple string, say \"

Answer 1

The good answer above throws a warning. You can also do:

df.insert(0, 'A', 'foo')

where 0 is the index where the new column will be inserted.

Answer 2

Just select the column and assign like normal:

In [194]:
df['A'] = 'foo'
df

Out[194]:
     A
0  foo
1  foo
2  foo
3  foo

Assigning a scalar value will set all the rows to the same scalar value