# NumPy Data Types

## Data Types in Python

By default Python have these data types:

• `strings` - used to represent text data, the text is given under quote marks. e.g. "ABCD"
• `integer` - used to represent integer numbers. e.g. -1, -2, -3
• `float` - used to represent real numbers. e.g. 1.2, 42.42
• `boolean` - used to represent True or False.
• `complex` - used to represent complex numbers. e.g. 1.0 + 2.0j, 1.5 + 2.5j

## Data Types in NumPy

NumPy has some extra data types, and refer to data types with one character, like `i` for integers, `u` for unsigned integers etc.

Below is a list of all data types in NumPy and the characters used to represent them.

• `i` - integer
• `b` - boolean
• `u` - unsigned integer
• `f` - float
• `c` - complex float
• `m` - timedelta
• `M` - datetime
• `O` - object
• `S` - string
• `U` - unicode string
• `V` - fixed chunk of memory for other type ( void )

## Checking the Data Type of an Array

The NumPy array object has a property called `dtype` that returns the data type of the array:

### Example

Get the data type of an array object:

import numpy as np

arr = np.array([1, 2, 3, 4])

print(arr.dtype)
Try it Yourself »

### Example

Get the data type of an array containing strings:

import numpy as np

arr = np.array(['apple', 'banana', 'cherry'])

print(arr.dtype)
Try it Yourself »

## Creating Arrays With a Defined Data Type

We use the `array()` function to create arrays, this function can take an optional argument: `dtype` that allows us to define the expected data type of the array elements:

### Example

Create an array with data type string:

import numpy as np

arr = np.array([1, 2, 3, 4], dtype='S')

print(arr)
print(arr.dtype)
Try it Yourself »

For `i`, `u`, `f`, `S` and `U` we can define size as well.

### Example

Create an array with data type 4 bytes integer:

import numpy as np

arr = np.array([1, 2, 3, 4], dtype='i4')

print(arr)
print(arr.dtype)
Try it Yourself »

## What if a Value Can Not Be Converted?

If a type is given in which elements can't be casted then NumPy will raise a ValueError.

ValueError: In Python ValueError is raised when the type of passed argument to a function is unexpected/incorrect.

### Example

A non integer string like 'a' can not be converted to integer (will raise an error):

import numpy as np

arr = np.array(['a', '2', '3'], dtype='i')
Try it Yourself »

## Converting Data Type on Existing Arrays

The best way to change the data type of an existing array, is to make a copy of the array with the `astype()` method.

The `astype()` function creates a copy of the array, and allows you to specify the data type as a parameter.

The data type can be specified using a string, like `'f'` for float, `'i'` for integer etc. or you can use the data type directly like `float` for float and `int` for integer.

### Example

Change data type from float to integer by using `'i'` as parameter value:

import numpy as np

arr = np.array([1.1, 2.1, 3.1])

newarr = arr.astype('i')

print(newarr)
print(newarr.dtype)
Try it Yourself »

### Example

Change data type from float to integer by using `int` as parameter value:

import numpy as np

arr = np.array([1.1, 2.1, 3.1])

newarr = arr.astype(int)

print(newarr)
print(newarr.dtype)
Try it Yourself »

### Example

Change data type from integer to boolean:

import numpy as np

arr = np.array([1, 0, 3])

newarr = arr.astype(bool)

print(newarr)
print(newarr.dtype)
Try it Yourself »

## Exercise:

NumPy uses a character to represent each of the following data types, which one?

```i = integer
= boolean
= unsigned integer
= float
= complex float
= timedelta
= datetime
= object
= string
```

Start the Exercise

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