According to the Format Specification Mini-Language you have to specify it before the "align":

contents = [('Introduction', 1), ('Python Basics', 5),
            ('Creating Your First Program', 12),
            ('Operators and Variables', 29)]

row_length = 35

for chapt, page in contents:
    dots = str(row_length - len(str(page)))
    print(f"{chapt:.<{dots}}{page}")

*This is now independent of the page number's length. A little bit more flexible.

Here is another way how you can format using 'f-string' format:

print(
    f"{'Trades:':<15}{cnt:>10}",
    f"{'Wins:':<15}{wins:>10}",
    f"{'Losses:':<15}{losses:>10}",
    f"{'Breakeven:':<15}{evens:>10}",
    f"{'Win/Loss Ratio:':<15}{win_r:>10}",
    f"{'Mean Win:':<15}{mean_w:>10}",
    f"{'Mean Loss:':<15}{mean_l:>10}",
    f"{'Mean:':<15}{mean_trd:>10}",
    f"{'Std Dev:':<15}{sd:>10}",
    f"{'Max Loss:':<15}{max_l:>10}",
    f"{'Max Win:':<15}{max_w:>10}",
    f"{'Sharpe Ratio:':<15}{sharpe_r:>10}",
    sep="\n"
)

This will provide the following output:

Trades:              2304
Wins:                1232
Losses:              1035
Breakeven:             37
Win/Loss Ratio:      1.19
Mean Win:           0.381
Mean Loss:         -0.395
Mean:               0.026
Std Dev:             0.56
Max Loss:          -3.406
Max Win:             4.09
Sharpe Ratio:      0.7395

What you are doing here is you are saying that the first column is 15 chars long and it's left-justified and the second column (values) is 10 chars long and it's right-justified.

If you joining items from the list and you want to format space between items you can use `` and regular formatting techniques.

This example separates each number by 3 spaces. The key here is f"{'':>3}"

print(f"{'':>3}".join(str(i) for i in range(1, 11)))

output:

1   2   3   4   5   6   7   8   9   10

This version uses the str.format method.

Python 2.7 and newer

sys.stdout.write("{:<7}{:<51}{:<25}\n".format(code, name, industry))

Python 2.6 version

sys.stdout.write("{0:<7}{1:<51}{2:<25}\n".format(code, name, industry))

UPDATE

Previously there was a statement in the docs about the % operator being removed from the language in the future. This statement has been removed from the docs.