What does "days += 1" mean in Python?

Question

I cannot follow this code, and was hoping someone can explain it to me

def negative(temperatures):
    days = 0
    for t in temperatures:
        if t < 0:
            days += 1
    return days

Can someone please explain line 5?

So from what I understand the function scans for negative temperatures in the array 'temperatures', assigns the first index that is <0 to t, and then line 5 takes days, which = 0, and then adds 1 to it, why does this equal one?

Possible duplicate of [What does it mean += in Python?](https://stackoverflow.com/questions/7721192/what-does-it-mean-in-python) — Georgy, May 22 '19 at 08:58

ncica · Accepted Answer · 2019-04-16T11:14:16.963

Notionally a += b "adds" b to a,storing the result in a.

Syntax:

A += B

A: Any valid object.

B: Any valid object.

Equivalent to A = A + B.

days += 1

is the same as

days = days + 1

Note:

you are using here variable days like "counter" (you are counting how much days had temterature <0)

you have list of temperatures ,probably something like : temperatures = [3,18,-2,4,-6]

you are passing over all items in your list temperatures:

for t in temperatures:

you are checking every item if its less than 0:

if t < 0:

if temperature is negative: variable days(started from 0) will increase for 1

for exemple: in first step days = 0

days = days + 1 -> 0+1 = 1

in next step days = 1

days = days + 1 -> 1+1 = 2

in next step days = 2

days = days + 1 -> 2+1 = 3

NOTE : difference between = and ==

OPERATOR = Assign value of right side of expression to left side operand, its not relational operators which compare if both operands are equal, that is ==

example:

myNumber = 5

This assigns 5 to variable myNumber.

if (myNumber == 5):
   print(myNumber)

This tests for equality. The two use are not interchangeable.

What does "days += 1" mean in Python?

1 Answers1