# If Statement

Python supports the usual logical conditions from mathematics:

* Equals: a == b
* Not Equals: a != b
* Less than: a < b
* Less than or equal to: a <= b
* Greater than: a > b
* Greater than or equal to: a >= b

```
if <expression>:
    Statements
```

### Indentation

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose

```
# wrong indentation 
if <expression>:
Statements
```

### Elif

The elif keyword is pythons way of saying "if the previous conditions were not true, then try this condition".

```
if <expression>:
    Statements
elif <expression>:
    Statements
```

```
a = 33
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
Output: a and b are equal
```

### Else

The else keyword catches anything which isn't caught by the preceding conditions.

```
a = 200
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
else:
  print("a is greater than b")
Output: a is greater than b
```

You can also have an `else` without the `elif`:

### Short Hand If

```
if a > b: print("a is greater than b")
```

### Short Hand If ... Else

```
a = 2
b = 330
print("A") if a > b else print("B")
```

### logical operators

#### And

The and keyword is a logical operator, and is used to combine conditional statements:

```
a = 200
b = 33
c = 500
if a > b and c > a:
  print("Both conditions are True")
```

#### Or

```
a = 200
b = 33
c = 500
if a > b or a > c:
  print("At least one of the conditions is True")
```

### Nested If

```
x = 41

if x > 10:
  print("Above ten,")
  if x > 20:
    print("and also above 20!")
  else:
    print("but not above 20.")
```

### The pass Statement

`if` statements cannot be empty, but if you for some reason have an `if` statement with no content, put in the `pass` statement to avoid getting an error.

```
a = 33
b = 200

if b > a:
  pass
```

[source](https://www.w3schools.com/python/python_while_loops.asp)