Detailed explanation of the related uses of array array module in Python-Python Tutorial-php.cn

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Detailed explanation of the related uses of array array module in Python

Jul 22, 2016 am 08:56 AM

array python array

Initialization
Array instantiation can provide a parameter to describe the allowed data type, and can also have an initial data sequence stored in the array.

import array
import binascii
s = 'This is the array.'
a = array.array('c', s)
print 'As string:', s
print 'As array :', a
print 'As hex  :', binascii.hexlify(a)

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The array is configured to contain a sequence of bytes, initialized with a simple string.

&gt;&gt;&gt; ================================ RESTART ================================
&gt;&gt;&gt; 
As string: This is the array.
As array : array('c', 'This is the array.')
As hex  : 54686973206973207468652061727261792e

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Processing Arrays
Similar to other python sequences, arrays can be expanded and processed in the same way.

import array
import pprint
a = array.array('i', xrange(3))
print 'Initial :', a
a.extend(xrange(3))
print 'Extended:', a
print 'slice: :', a[2:5]
print 'Itetator:'
print list(enumerate(a))

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Supported operations include sharding, iteration, and adding elements to the end.

&gt;&gt;&gt; ================================ RESTART ================================
&gt;&gt;&gt; 
Initial : array('i', [0, 1, 2])
Extended: array('i', [0, 1, 2, 0, 1, 2])
slice: : array('i', [2, 0, 1])
Itetator:
[(0, 0), (1, 1), (2, 2), (3, 0), (4, 1), (5, 2)]

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Arrays and files
The contents of an array can be written to a file or an array read from a file using dedicated built-in methods for efficient reading/writing of files.

import array
import binascii
import tempfile

a = array.array('i', xrange(5))
print 'A1: ',a
output = tempfile.NamedTemporaryFile()
a.tofile(output.file)
output.flush

with open(output.name, 'rb') as input:
  raw_input = input.read()
  print 'Raw Contents:', binascii.hexlify(raw_data)

  input.seek(0)
  a2 = array.array('i')
  a2.fromfile(input, len(a))
  print 'A2: ', a2

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Candidate Byte Order
If the data in the array is not in inherent byte order, or needs to be swapped before being sent to a system with a different byte order, you can convert the entire array in python without iterating through each element.

import array
import binascii

def to_hex(a):
  chars_per_item = a.itemsize * 2
  hex_version = binascii.hexlify(a)
  num_chunks = len(hex_version) / chars_per_item
  for i in xrange(num_chunks):
    start = i * chars_per_item
    end = start + chars_per_item
    yield hex_version[start:end]

a1 = array.array('i', xrange(5))
a2 = array.array('i', xrange(5))
a2.byteswap()

fmt = '%10s %10s %10s %10s'
print fmt % ('A1_hex', 'A1', 'A2_hex', 'A2')
print fmt % (('-' * 10,) * 4)
for value in zip(to_hex(a1), a1, to_hex(a2), a2):
  print fmt % value

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byteswap() will swap the byte order of elements in the C array, which is much more efficient than looping through data in python.

&gt;&gt;&gt; ================================ RESTART ================================
&gt;&gt;&gt; 
  A1_hex     A1   A2_hex     A2
---------- ---------- ---------- ----------
 00000000     0  00000000     0
 01000000     1  00000001  16777216
 02000000     2  00000002  33554432
 03000000     3  00000003  50331648
 04000000     4  00000004  67108864

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