Python Arrays
Note: Python does not have built-in support for Arrays, but Python Lists can be used instead.
Arrays
Note: This page shows you how to use LISTS as ARRAYS, however, to work with arrays in Python you will have to import a library, like the NumPy library.
Arrays are used to store multiple values in one single variable:
Example
Create an array containing car names:
What is an Array?
An array is a special variable, which can hold more than one value at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:
However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
An array can hold many values under a single name, and you can access the values by referring to an index number.
Access the Elements of an Array
You refer to an array element by referring to the index number.
Example
Get the value of the first array item:
Example
Modify the value of the first array item:
The Length of an Array
Use the len() method to return the length of an array (the number of elements in an array).
Example
Return the number of elements in the cars array:
Note: The length of an array is always one more than the highest array index.
Looping Array Elements
You can use the for in loop to loop through all the elements of an array.
Example
Print each item in the cars array:
Adding Array Elements
You can use the append() method to add an element to an array.
Example
Add one more element to the cars array:
Removing Array Elements
You can use the pop() method to remove an element from the array.
Example
Delete the second element of the cars array:
You can also use the remove() method to remove an element from the array.
Example
Delete the element that has the value «Volvo»:
Note: The list’s remove() method only removes the first occurrence of the specified value.
Array Methods
Python has a set of built-in methods that you can use on lists/arrays.
| Method | Description |
|---|---|
| append() | Adds an element at the end of the list |
| clear() | Removes all the elements from the list |
| copy() | Returns a copy of the list |
| count() | Returns the number of elements with the specified value |
| extend() | Add the elements of a list (or any iterable), to the end of the current list |
| index() | Returns the index of the first element with the specified value |
| insert() | Adds an element at the specified position |
| pop() | Removes the element at the specified position |
| remove() | Removes the first item with the specified value |
| reverse() | Reverses the order of the list |
| sort() | Sorts the list |
Note: Python does not have built-in support for Arrays, but Python Lists can be used instead.
array — Efficient arrays of numeric values¶
This module defines an object type which can compactly represent an array of basic values: characters, integers, floating point numbers. Arrays are sequence types and behave very much like lists, except that the type of objects stored in them is constrained. The type is specified at object creation time by using a type code, which is a single character. The following type codes are defined:
- It can be 16 bits or 32 bits depending on the platform.
Changed in version 3.9: array(‘u’) now uses wchar_t as C type instead of deprecated Py_UNICODE . This change doesn’t affect its behavior because Py_UNICODE is alias of wchar_t since Python 3.3.
The actual representation of values is determined by the machine architecture (strictly speaking, by the C implementation). The actual size can be accessed through the array.itemsize attribute.
The module defines the following item:
A string with all available type codes.
The module defines the following type:
class array. array ( typecode [ , initializer ] ) ¶
A new array whose items are restricted by typecode, and initialized from the optional initializer value, which must be a list, a bytes-like object , or iterable over elements of the appropriate type.
If given a list or string, the initializer is passed to the new array’s fromlist() , frombytes() , or fromunicode() method (see below) to add initial items to the array. Otherwise, the iterable initializer is passed to the extend() method.
Array objects support the ordinary sequence operations of indexing, slicing, concatenation, and multiplication. When using slice assignment, the assigned value must be an array object with the same type code; in all other cases, TypeError is raised. Array objects also implement the buffer interface, and may be used wherever bytes-like objects are supported.
Raises an auditing event array.__new__ with arguments typecode , initializer .
The typecode character used to create the array.
The length in bytes of one array item in the internal representation.
Append a new item with value x to the end of the array.
Return a tuple (address, length) giving the current memory address and the length in elements of the buffer used to hold array’s contents. The size of the memory buffer in bytes can be computed as array.buffer_info()[1] * array.itemsize . This is occasionally useful when working with low-level (and inherently unsafe) I/O interfaces that require memory addresses, such as certain ioctl() operations. The returned numbers are valid as long as the array exists and no length-changing operations are applied to it.
When using array objects from code written in C or C++ (the only way to effectively make use of this information), it makes more sense to use the buffer interface supported by array objects. This method is maintained for backward compatibility and should be avoided in new code. The buffer interface is documented in Buffer Protocol .
“Byteswap” all items of the array. This is only supported for values which are 1, 2, 4, or 8 bytes in size; for other types of values, RuntimeError is raised. It is useful when reading data from a file written on a machine with a different byte order.
Return the number of occurrences of x in the array.
Append items from iterable to the end of the array. If iterable is another array, it must have exactly the same type code; if not, TypeError will be raised. If iterable is not an array, it must be iterable and its elements must be the right type to be appended to the array.
Appends items from the string, interpreting the string as an array of machine values (as if it had been read from a file using the fromfile() method).
New in version 3.2: fromstring() is renamed to frombytes() for clarity.
Read n items (as machine values) from the file object f and append them to the end of the array. If less than n items are available, EOFError is raised, but the items that were available are still inserted into the array.
Append items from the list. This is equivalent to for x in list: a.append(x) except that if there is a type error, the array is unchanged.
Extends this array with data from the given unicode string. The array must be a type ‘u’ array; otherwise a ValueError is raised. Use array.frombytes(unicodestring.encode(enc)) to append Unicode data to an array of some other type.
Return the smallest i such that i is the index of the first occurrence of x in the array. The optional arguments start and stop can be specified to search for x within a subsection of the array. Raise ValueError if x is not found.
Changed in version 3.10: Added optional start and stop parameters.
Insert a new item with value x in the array before position i. Negative values are treated as being relative to the end of the array.
Removes the item with the index i from the array and returns it. The optional argument defaults to -1 , so that by default the last item is removed and returned.
Remove the first occurrence of x from the array.
Reverse the order of the items in the array.
Convert the array to an array of machine values and return the bytes representation (the same sequence of bytes that would be written to a file by the tofile() method.)
New in version 3.2: tostring() is renamed to tobytes() for clarity.
Write all items (as machine values) to the file object f.
Convert the array to an ordinary list with the same items.
Convert the array to a unicode string. The array must be a type ‘u’ array; otherwise a ValueError is raised. Use array.tobytes().decode(enc) to obtain a unicode string from an array of some other type.
When an array object is printed or converted to a string, it is represented as array(typecode, initializer) . The initializer is omitted if the array is empty, otherwise it is a string if the typecode is ‘u’ , otherwise it is a list of numbers. The string is guaranteed to be able to be converted back to an array with the same type and value using eval() , so long as the array class has been imported using from array import array . Examples:
array('l') array('u', 'hello \u2641') array('l', [1, 2, 3, 4, 5]) array('d', [1.0, 2.0, 3.14])
Packing and unpacking of heterogeneous binary data.
Packing and unpacking of External Data Representation (XDR) data as used in some remote procedure call systems.
The NumPy package defines another array type.