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.
Remove Element from an Array/List in Python
This tutorial will go through some common ways for removing elements from Python arrays/lists.
Arrays or Lists?
Python’s built-in sequence representation is a list, defined as a heterogenous sequence of elements, where each element has a definitive index in the sequence. To use arrays, you’d have to import the array module, which does ship with Python itself, but lists are far more commonly used.
Additionally — since the list syntax looks a lot like the syntax you’d use to define arrays in other programming languages — the terms «array» and «list» are oftentimes used interchangeably, even though they’re not the same data structure. It’s worth noting that many of these methods work both for an array and a list!
Using remove()
Appropriately, the remove() function can be used on any array or list in Python. To use it, we can simply pass the value of the element we want to remove. Let’s imagine we have the following array:
array = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100] To remove, say, element 40 , we would simply write:
The result is the same array without the value 40 :
[10, 20, 30, 50, 60, 70, 80, 90, 100] Using pop()
The pop() function accepts the index of the element we want to remove. If we had the same array/list as before (with values from 10 to 100), we could write something like the following:
If we printed the result of the pop method, it would be the value 40 :
[10, 20, 30, 50, 60, 70, 80, 90, 100] Similarly to how pop() works in the stack data structure, here pop() also returns the value that it had just removed.
The only difference is that with arrays, we can remove an arbitrary element. With stacks, only the top element (i.e. the last one added) can ever be removed.
Using del
del is a python keyword used for deleting objects. Its exact behavior changes depending on the context, so we can also use it to remove list elements, though, arrays don’t support this. Once again, let’s take the same array and index as before:
array = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100] index = 3 To remove the element at index 3 , we simply type the following:
If we now printed the contents of our array, we would get the following output:
[10, 20, 30, 50, 60, 70, 80, 90, 100] Using numpy Arrays
NumPy arrays are commonly used (especially in machine learning), so let’s show one of the ways to remove an element from a numpy array. Before using numpy , it is necessary to import it with:
To create a numpy array, we can wrap our current list using np.array() as such:
Alternatively, we could also declare a new array inside the method call itself:
a = np.array([10, 20, 30, 40, 50, 60, 70, 80, 90, 100]) Now to remove an element at index 3 , we use the following code:
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index = 3 a = np.delete(a, index) delete() is a static method declared in the numpy module. It accepts the array and the index of the element to remove.
The method returns a new array without the removed element:
[10, 20, 30, 50, 60, 70, 80, 90, 100] Conclusion
There are different ways to remove a list element in Python. Sometimes we might want to remove an element by index and sometimes by value. Sometimes we’re using Python’s default array and sometimes a numpy array.
In all these cases, it’s good to have multiple options to help us decide which of the techniques to use.
Python Remove Array Item
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.
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