# Sum of numbers from 0 to N in Python

## The challenge

We want to generate a function that computes the series starting from 0 and ending until the given number.

## Example:

**Input:** > 6

**Output:** 0+1+2+3+4+5+6 = 21

**Input:** > -15

**Output:** -15<0

**Input:** > 0

**Output:** 0=0

## The solution in Python code

Option 1:

```
def show_sequence(n):
if n == 0:
return "0=0"
elif n < 0:
return str(n) + "<0"
else:
counter = sum(range(n+1))
return '+'.join(map(str, range(n+1))) + " = " + str(counter)
```

Option 2:

```
def show_sequence(n):
s = '0'
for i in range(1, n+1):
s+='+'+str(i)
return s+' = '+str(n*(n+1)//2) if n>0 else '0=0' if n==0 else str(n)+'<0'
```

Option 3:

```
def show_sequence(n):
if n < 0:
return str(n) + "<0"
if n == 0:
return str(n) + "=0"
summ = sum(range(n+1))
numstr = "+".join(map(str, range(n+1)))
return numstr + " = " + str(summ)
```

## Test cases to validate our solution

```
import test
from solution import show_sequence
@test.describe("Fixed Tests")
def fixed_tests():
@test.it('Basic Test Cases')
def basic_test_cases():
tests = (
(6, "0+1+2+3+4+5+6 = 21"),
(7, "0+1+2+3+4+5+6+7 = 28"),
(0, "0=0"),
(-1, "-1<0"),
(-10, "-10<0"),
)
for inp, exp in tests:
test.assert_equals(show_sequence(inp), exp)
@test.describe("Random Tests")
def _():
from random import randint
def reference(n):
if n < 0:
return "%s<0" % n
if n == 0:
return "0=0"
return "%s = %s" % ("+".join(map(str, range(0, n+1))), n * (n + 1) // 2)
for _ in range(100):
test_case = randint(-100, 101)
@test.it(f"testing for show_sequence({test_case})")
def test_case():
test.assert_equals(show_sequence(test_case),reference(test_case))
```