#! /usr/bin/env python3
#
def python_text_files ( ):

  import matplotlib.pyplot as plt
  import numpy as np

  print ( '' )
  print ( 'python_text_files():' )
  print ( '  Exercises for reading and writing files.' )
#
#  Write a text file for a single array.
#
  print ( '' )
  print ( '  Use np.savetxt() to write an array to a text file.' )
  print ( '' )
  filename = 'hilbert_matrix.txt'
  H = np.zeros ( [ 5, 5 ] )
  for i in range ( 0, 5 ):
    for j in range ( 0, 5 ):
      H[i,j] = 1 / ( i + j + 1 )
  np.savetxt ( filename, H )
  print ( '  Created the text file "' + filename + '"' )
#
#  Use np.loadtxt() to read a table from a text file.
#  All the data items must be of the same type.
#
  print ( '' )
  print ( '  Use np.loadtxt() to read a table of data from a text file.' )
  print ( '' )
  filename = 'hilbert_matrix.txt'
  data = np.loadtxt ( filename )
  m, n = data.shape
  print ( 'The table in "' + filename + '" has ' + str ( m ) + ' rows and ' + str ( n ) + ' columns.' )
  print ( 'The maximum entries in each column:' )
  print ( np.max ( data, axis = 0 ) )
#
#  Write a text file one line at a time.
#
  print ( '' )
  print ( '  Use open(), .write(), and .close() to create a text file.' )
  print ( '' )
  filename = 'mystery.txt'
  output = open ( 'mystery.txt', 'w' )
  output.write ( 'Yesterday, upon the stair,\n' )
  output.write ( 'I met a man who wasn\'t there.\n' )
  output.write ( 'He wasn\'t there again today\n' )
  output.write ( 'I wish, I wish he\'d go away.\n' )
  output.close()
  print ( '  Wrote the text file "' + filename + '"' )
#
#  Read the text file.
#
  print ( '' )
  print ( '  Use open(), .write(), and .close() to read a text file.' )
  print ( '' )
  print ( '  Contents of "' + filename + '"' )
  print ( '' )
  input = open ( filename, 'r' )
  for line in input:
    print ( line, end = '' )
  input.close ( )
#
#  Append more data to the text file.
#
  print ( '' )
  print ( '  Use the append mode in open() to add lines to an existing file.' )
  print ( '' )
  output = open ( 'mystery.txt', 'a' )
  output.write ( '\n' )
  output.write ( 'When I came home last night at three\n' )
  output.write ( 'The man was waiting there for me\n' )
  output.write ( 'But when I looked around the hall\n' )
  output.write ( 'I couldn\'t see him there at all!\n' )
  output.close()
  print ( '  More lines were added to "' + filename + '"' )
#
#  Use .split() to read individual words from a line of a file.
#
  print ( '' )
  print ( '  Use .split() to read words from lines from text file.' )
  print ( '' )

  filename = 'patient.txt'
  output = open ( 'patient.txt', 'w' )
  output.write ( 'Alice 60 120.3\n' )
  output.write ( 'Bob 65 200.5\n' )
  output.write ( 'Carol 70 160.1\n' )
  output.close()
  print ( '  Wrote the text file "' + filename + '"' )
  print ( '' )
  bio = open ( filename, 'r' )
  for line in bio:
    w = line.split()
    name = w[0]
    height = int ( w[1] )
    weight = float ( w[2] )
    bmi = ( weight / 2.204 ) * ( 39.370 / height )**2
    print ( name, height, weight, bmi )
  bio.close ( )
#
#  Texting while deriving.
#
  print ( '' )
  print ( '  Texting while deriving.' )
  print ( '' )
  filename = 'divisors.txt'
  output = open ( filename, 'w' )
  for n in range ( 1, 21 ):
    for i in range ( 1, n + 1 ):
      if ( ( n % i ) == 0 ):
        output.write ( ' ' + str ( i ) )
    output.write ( '\n' )
  output.close ( )
  print ( '  Wrote file "' + filename + '"' )
#
#  Read lists of varying length.
#
  print ( '' )
  print ( '  Read lists of varying length.' )
  print ( '' )
  divisors = []
  filename = 'divisors.txt'
  output = open ( filename, 'r' )
  for line in output:
    w = line.split()
    for i in range ( 0, len ( w ) ):
      w[i] = int ( w[i] )
    divisors.append ( w )
  output.close ( )
  print ( divisors )
#
#  Write several data items of different length and type.
#
  print ( '' )
  print ( '  Write several data items of different length and type' )
  print ( '' )
  A = np.array ( [ \
    [ 11.0, 12.0,  0.0,  0.0, 15.0 ], \
    [ 21.0, 22.0,  0.0,  0.0,  0.0 ], \
    [  0.0,  0.0, 33.0,  0.0, 35.0 ], \
    [  0.0,  0.0,  0.0, 44.0,  0.0 ], \
    [ 51.0,  0.0, 53.0,  0.0, 55.0 ] ] )
  b = np.array ( [ 110.0, 65.0, 274.0, 176.0, 485.0 ] )
  x = np.array ( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] )
  filename = 'slap_matrix.txt'
  n = 5
  nz = 11
  sym = 0
  rhs_given = 1
  x_given = 1
  output = open ( filename, 'w' )
  output.write ( str ( n ) + ' ' )
  output.write ( str ( nz ) + ' ' )
  output.write ( str ( sym ) + ' ' )
  output.write ( str ( rhs_given ) + ' ' )
  output.write ( str ( x_given ) + '\n' )
  for i in range ( 0, n ):
   for j in range ( 0, n ):
      if ( A[i,j] != 0.0 ):
        output.write ( str ( i ) + ' ' + str ( j ) + ' ' + str ( A[i,j] ) + '\n' )
  for i in range ( 0, n ):
    output.write ( str ( b[i] ) + '\n' )
  for i in range ( 0, n ):
    output.write ( str ( x[i] ) + '\n' )
  output.close()
  print ( '  Created file"' + filename + '"' )
#
#  Read several data items of different length and type.
#
  print ( '' )
  print ( '  Carefully read lines of varying length and type.' )
  print ( '' )
  filename = 'slap_matrix.txt'
  input = open ( filename, 'r' )
  stage = 'read_size'
  for line in input:
    w = line.split()
    if ( stage == 'read_size' ):
      n = int ( w[0] )
      nz = int ( w[1] )
      sym = int ( w[2] )
      rhs_given = int ( w[3] )
      x_given = int ( w[4] )
      stage = 'read_matrix'
      iz = 0
      A = np.zeros ( [ n, n ] )
    elif ( stage == 'read_matrix' ):
      i = int ( w[0] )
      j = int ( w[1] )
      aij = float ( w[2] )
      A[i,j] = aij
      iz = iz + 1
      if ( nz <= iz ):
        if ( rhs_given == 0 ):
          break
        else:
          stage = 'read_rhs'
          b = np.zeros ( n )
          i = 0
    elif ( stage == 'read_rhs' ):
      b[i] = float ( w[0] )
      i = i + 1
      if ( n <= i ):
        if ( x_given == 0 ):
          break
        else:
          stage = 'read_x'
          x = np.zeros ( n )
          i = 0
    elif ( stage == 'read_x' ):
      x[i] = float ( w[0] )
      i = i + 1
      if ( n <= i ):
        break
     
  input.close ( )
  print ( '  Matrix A:' )
  print ( A )
  print ( '  RHS b:' )
  print ( b )
  print ( '  Solution x:' )
  print ( x )
  Ax = np.dot ( A, x )
  print ( '  Verify: A*x = ' )
  print ( Ax )

  return

if ( __name__ == "__main__" ):
  python_text_files ( )