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# Understanding a for loop

A `for` loop is one of the most used loops in many computer languages. The following flow diagram demonstrates how a loop works. Usually, we start with an initial value. Then, we test a condition. If the condition is false, the program stops. Otherwise, we execute a set of commands:

The simplest example is given as follows:

```>>>for i in range(1,5):
print i
```

Running these two lines will print 1, 2, 3, and 4. We have to be careful with the `range()` function since the last number, 5, will not be printed in Python. Thus, if we intend to print from 1 to n, we have to use the following code:

```>>>n=10
>>>for i in range(1,n+1):
print ...```

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