Using Python String Formatting with Changing Lists Sizes

Question

how do I print the string line without preparing from advance the {} places. Because now my function needed only 6 places, but if I'll change the input (n,m) I'll need different number of {}. How to define it?

def all_pairs_sum(m,n):
    sum = 0
    mult = []
    for m in range(1,m+1):
        for n in range(1,n+1):
            l = m*n
            mult.append(l)
            sum = sum + m*n
            print(m," * ", n, " = ", l)
    print("{}+{}+{}+{}+{}+{} =".format(*mult))
    return sum

print (all_pairs_sum(2,3))

'+'.join(mult)?

TrebledJ
– TrebledJ

2019-02-17 08:06:26 +00:00
Commented Feb 17, 2019 at 8:06 — TrebledJ
– TrebledJ, Commented Feb 17, 2019 at 8:06

Vlad Bezden · Accepted Answer · 2019-02-17 09:42:13Z

1

You can use f-string feature added in Python 3.6. Also notice that sum is a function from Python standard library. It's better not to name your variables that name. As you can see in my example I called it total

def all_pairs_sum(m,n):
    total = 0
    mult = []
    for m in range(1, m + 1):
      for n in range(1 , n + 1):
          l = m * n
          mult.append(l)
          total += l
          print(f"{m} * {n} = {l:>2d}")
    print(f"{' + '.join(map(str, mult))} = {sum(mult)}")
    return total

print(all_pairs_sum(2, 5))

Output:

1 * 1 =  1
1 * 2 =  2
1 * 3 =  3
1 * 4 =  4
1 * 5 =  5
2 * 1 =  2
2 * 2 =  4
2 * 3 =  6
2 * 4 =  8
2 * 5 = 10
1 + 2 + 3 + 4 + 5 + 2 + 4 + 6 + 8 + 10 = 45
45

edited Feb 17, 2019 at 9:42

answered Feb 17, 2019 at 9:31

Vlad Bezden

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Comments

Mykola Zotko · Accepted Answer · 2019-02-17 08:46:59Z

1

If you use the method format() you have a definite number of replacement fields {}. You can use this solution:

l = list(range(5))
print(' + '.join(str(i) for i in l), ' = ', sum(l))
# 0 + 1 + 2 + 3 + 4  =  10

answered Feb 17, 2019 at 8:46

Mykola Zotko

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Comments

balderman · Accepted Answer · 2019-02-17 08:09:04Z

0

How about:

def get_msg_template(n):
    tmp =  '{}+' * n
    return tmp[:-1]

print(get_msg_template(4))

Output:

 {}+{}+{}+{}

answered Feb 17, 2019 at 8:09

balderman

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2 Comments

Andrey Semakin Over a year ago

You also can use join here: ' + '.join(['{}'] * n)

V.H Over a year ago

also helps. I used for my code print(' + '.join(['{}'] * n*m).format(*mult))

abolotnov · Accepted Answer · 2019-02-17 08:12:47Z

0

If you are looking for printing out the string representation of summed values, you can use something like this:

print("+".join(str(x) for x in mult))

answered Feb 17, 2019 at 8:12

abolotnov

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