Python appending to array

Python add elements to an Array

Python doesn’t have a specific data type to represent arrays.

The following can be used to represent arrays in Python:

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1. Adding to an array using Lists

If we are using List as an array, the following methods can be used to add elements to it:

• By using append() function : It adds elements to the end of the array.
• By using insert() function : It inserts the elements at the given index.
• By using extend() function : It elongates the list by appending elements from both the lists.

Example 1: Adding elements to an array using append() function

my_input = ['Engineering', 'Medical'] my_input.append('Science') print(my_input)

[‘Engineering’, ‘Medical’, ‘Science’]

Example 2: Adding elements to an array using extend() function

my_input = ['Engineering', 'Medical'] input1 = [40, 30, 20, 10] my_input.extend(input1) print(my_input)

[‘Engineering’, ‘Medical’, 40, 30, 20, 10]

Example 3: Adding elements to an array using insert() function

my_input = [1, 2, 3, 4, 5] print(f'Current Numbers List ') number = int(input("Please enter a number to be added:\n")) index = int(input(f'Enter the index between 0 and to add the given number:\n')) my_input.insert(index, number) print(f'Updated List ')

2. Adding to an array using array module

If we are using the array module, the following methods can be used to add elements to it:

• By using + operator : The resultant array is a combination of elements from both the arrays.
• By using append() function : It adds elements to the end of the array.
• By using insert() function : It inserts the elements at the given index.
• By using extend() function : It elongates the list by appending elements from both the lists.

import array s1 = array.array('i', [1, 2, 3]) s2 = array.array('i', [4, 5, 6]) print(s1) print(s2) s3 = s1 + s2 print(s3) s1.append(4) print(s1) s1.insert(0, 10) print(s1) s1.extend(s2) print(s1)

3. Addition of elements to NumPy array

We can add elements to a NumPy array using the following methods:

• By using append() function : It adds the elements to the end of the array.
• By using insert() function : It adds elements at the given index in an array.

import numpy # insert function arr1_insert = numpy.array([1, 23, 33]) arr2_insert = numpy.insert(arr1_insert, 1, 91) print(arr2_insert) # append function arr1_append = numpy.array([4, 2, 1]) arr2_append = numpy.append (arr1_append, [12, 13, 14]) print(arr2_append)

[ 1 91 23 33][ 4 2 1 12 13 14]

Conclusion

Thus, in this article, we have implemented possible ways to add elements to an array.

References

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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.

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How to append an Array in Python?

Hey, folks! In this article, we will focus on ways to append an array in Python.

What is Python Array?

In programming terms, an array is a linear data structure that stores similar kinds of elements.

As we all know, Python does not offer us with a specific data type — ‘array’. Rather, the following variants of Python Array are available for us to use–

• Python List: It contains all the functionalities of an Array.
• Python Array module: This module is used to create an array and manipulate the data with the specified functions.
• Python NumPy array: The NumPy module creates an array and is used for mathematical purposes.

Now, let us understand the ways to append elements to the above variants of Python Array.

Append an Array in Python Using the append() function

Python append() function enables us to add an element or an array to the end of another array. That is, the specified element gets appended to the end of the input array.

The append() function has a different structure according to the variants of Python array mentioned above.

Let us now understand the functioning of Python append() method on each variant of Python Array.

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Variant 1: Python append() function with Lists

Lists are considered as dynamic arrays. Python append() method can be framed here to add/append elements to the end of the list.

list.append(element or list)

The list or the element gets added to the end of the list and the list is updated with the added element.

lst = [10,20,30,40] x = [0,1,2] lst.append(x) print(lst)

Variant 2: Python append() method with the Array module

We can create an array using the Array module and then apply the append() function to add elements to it.

Initialize a Python array using the array module:

import array array.array('unicode',elements)

• unicode : It represents the type of elements to be occupied by the array. For example, ‘d’ represents double/float elements.

Further, the append() function operates in the same manner as that with Python Lists.

import array x = array.array('d', [1.4, 3.4]) y = 10 x.append(y) print(x)

Variant 3: Python append() method with NumPy array

The NumPy module can be used to create an array and manipulate the data against various mathematical functions.

Syntax: Python numpy.append() function

numpy.append(array,value,axis)

• array : It is the numpy array to which the data is to be appended.
• value : The data to be added to the array.
• axis (Optional): It specifies row-wise or column-wise operations.

In the below example, we have used numpy.arange() method to create an array within the specified range of values.

import numpy as np x = np.arange(3) print("Array x : ", x) y = np.arange(10,15) print("\nArray y : ", y) res = np.append(x, y) print("\nResult after appending x and y: ", res)

Array x : [0 1 2] Array y : [10 11 12 13 14] Result after appending x and y: [ 0 1 2 10 11 12 13 14]

Conclusion

That’s all for this topic. Feel free to comment below, in case you come across any doubt. For more such posts related to Python, do visit [email protected] .

References

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