As far as I can tell, tabulate doesn't seem to have an argument for this. Maybe look into prettytable, and especially the "Changing the appearance of your table - the hard way" chapter, that allows you to be more flexible with the table style.

EDIT: texttable may be useful too, as you can define the column width. The documentation seems to be a bit lacking though, and while the ease of use may be better, the modularity seems to be a bit worse at first glance.

Well, could this be what you need, it turns everything into 11 characters long text:

import pandas as pd

df = pd.DataFrame({'a': [12345, 2, 3], 'b': list('ABC')})
df = df.applymap(lambda x: str(x).ljust(11))
df.columns = df.columns.map(lambda x: str(x).ljust(11))
df.to_csv('somefile.txt', index=False)

I figured it out with a little poking around the pandas docs. This is what I'm doing now:

table = df[fields]
width = pandas.util.terminal.get_terminal_size() # find the width of the user's terminal window
pandas.set_option('display.width', width[0]) # set that as the max width in Pandas
print(table)