# If Statements

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&#x20;[Control Flow](http://python.swaroopch.com/control_flow.html)

Programs aren't very interesting when they only do one thing. We like programs to be multi-purposed and to accept inputs. In order to accomplish this we need some sort of control that allows us to switch on data.

## The if statement

If statements allow us to do something conditionally.

```python
if (condition):
    print('do something if our condition is true')
```

The if statement uses the reserved word `if` and then has parentheses which contain a condition. Only boolean values can go inside the parentheses. If that value is `True`, then the command(s) that are inside the if statement will be executed.

The if statement has a colon after the parentheses which indicates that a ***block*** is going to follow. The contents of the block are indented in Python. It is important that this indentation is consistent. If you indent your blocks by a single tab, then you must always do this. If you use four spaces then you must similarly always use 4 spaces. When you want to end the block then you simply go back to the indentation level you were at before the if.

```python
if (True):
    print("I'm inside the if")
print("I'm outside the if")
```

&#x20;*Try creating your own if statement!*

## Else

Sometimes we want to do something when a condition is `True` and something else when it is false. An else block allows you to switch on conditions like this:

```python
happy = True
if (happy):
    print("clap your hands")
else:
    print("stomp your feet")
```

You can also switch on multiple conditions using an `elif` (else if) statement. An `elif` is just like an `if` but comes after an initial `if`.

```python
mood = 'Grumpy'
if (mood == 'Morose');
    print("We should be friends")
elif (mood == 'Grumpy'):
    print("Don't be coming around me")
else:
    print("I guess I don't recognize your mood")
```

## Complex Examples

You can imagine more complex conditions where multiple variables come into play

```python
age = 11
mood = 'Grumpy'
family_member = True
if (mood == 'Morose' and age > 10 or family_member);
    print("We should be friends")
```

The above condition uses `and` and `or` to combine multiple conditions. When you say the whole statement out loud you can tell what should happen. In this case `mood` must be equal to `'Morose'` *and* `age` must be greater than 10. Since that combined condition is `False` we would not enter the if block. We have a third condition though. The `family_member` condition is also part of this and since there is an `or` combining the previous two conditions and this one, only one *or* the other is necessary to enter the block. Since `family_member` is `True` we will enter.

&#x20;*Try collecting some data from the user (input) and doing an if statement based on their response!*

## Tip

You might look at the `=` and `==` and wonder how they are different. The single `=` is used as the *assignment* operator. This operator assigns variables on the left of the sign to the value of whatever expression is on the right. The `==` operator is used to express boolean conditions. The two operands in this case must be exactly equal to be evaluated as True. `42 == "42"` may look like they are equal but they have different types. One is an `int` and the other is a `str`. Things can never be equal if they are of different types.