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.
Python | Move element to end of the list
The manipulation of lists is quite common in day-day programming. One can come across various issues where one wishes to perform using just one-liners. One such problem can be of moving a list element to the rear ( end of list ). Let’s discuss certain ways in which this can be done.
Method #1 : Using append() + pop() + index()
This particular functionality can be performed in one line by combining these functions. The append function adds the element removed by pop function using the index provided by index function.
Python3
The original list is : ['3', '5', '7', '9', '11'] The modified element moved list is : ['3', '7', '9', '11', '5']
Time Complexity: O(n), where n is the length of the list test_list
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the res list
Method #2: Using sort() + key = (__eq__)
The sort method can also be used to achieve this particular task in which we provide the key as equal to the string we wish to shift so that it is moved to the end.
Python3
The original list is : ['3', '5', '7', '9', '11'] The modified element moved list is : ['3', '7', '9', '11', '5']
Method #3 : Using remove() and insert() methods
Python3
The original list is : ['3', '5', '7', '9', '11'] The modified element moved list is : ['3', '7', '9', '11', '5']
Method #4 : Using list comprehension
Python3
Method #4 : Using del and ‘+’ operator
Python3
Step-by-step algorithm:
- Initialize the list test_list with the given input.
- Assign the value element to the variable element.
- Use the index() method to find the index of the element in the list that matches element. Assign the resulting index to the variable i.
- Use the del keyword to remove the element at the index i from the list.
- Use concatenation to add the updated element to the list.
- Assign the updated list to the variable test_list.
- Print the updated list.
Time complexity:
The time complexity of the algorithm is O(n), where n is the length of the input list test_list. The index() method has a linear time complexity with respect to the length of the list. The concatenation operation also has a linear time complexity with respect to the length of the list.
Auxiliary space complexity:
The auxiliary space complexity of the algorithm is O(1), constant. This is because the algorithm only creates a few variables to store the input list, the element to be updated, and the updated list. The size of these variables is independent of the size of the input list. Therefore, the space complexity of the algorithm is constant.
here’s an approach using collections.deque.rotate():
The collections.deque class in Python provides a rotate() method, which can be used to move elements in a list. We can convert our list into a deque, rotate it to move the desired element to the end, and then convert it back into a list.
Initialize the list and the element to be moved.
Convert the list to a deque using the collections.deque method.
Find the index of the element using the index() method.
Rotate the deque by the number of steps needed to move the element to the end using the rotate() method.
Convert the deque back to a list using the list() method.
Print the modified list.
Python: Append a new item to the end of the array
Write a Python program to append a new item to the end of the array.
Pictorial Presentation:
Sample Solution:
Python Code :
from array import * array_num = array('i', [1, 3, 5, 7, 9]) print("Original array: "+str(array_num)) print("Append 11 at the end of the array:") array_num.append(11) print("New array: "+str(array_num)) Original array: array('i', [1, 3, 5, 7, 9]) Append 11 at the end of the array: New array: array('i', [1, 3, 5, 7, 9, 11]) Python Code Editor:
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Python: Tips of the Day
Find current directory and file’s directory:
To get the full path to the directory a Python file is contained in, write this in that file:
import os dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won’t work if you’ve already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)
To get the current working directory use
Documentation references for the modules, constants and functions used above:
- The os and os.path modules.
- The __file__ constant
- os.path.realpath(path) (returns «the canonical path of the specified filename, eliminating any symbolic links encountered in the path»)
- os.path.dirname(path) (returns «the directory name of pathname path»)
- os.getcwd() (returns «a string representing the current working directory»)
- os.chdir(path) («change the current working directory to path»)
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