Differences

This shows you the differences between the selected revision and the current version of the page.

--- core:part9_answers 2010/03/20 15:16
+++ core:part9_answers 2010/04/18 08:00 current
@@ Line 1: / Line 1: @@
+=====9-1=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-1. File Filtering.
+# Author: PolyMath
+#
+def main():
+    text_file = open('test.txt')
+    lines = [line for line in text_file if line[0] != '#']  # dicard lines beginning with '#'
+    for line in lines:
+        if '#' in line:
+            idx = line.find('#')        # locate any other '#'
+            print(line[:idx])          # don't print the text after the '#'
+        else:
+            print(line.rstrip())       # here if no '#' found in the line of text.
+    print('\nDone!')
+#
+# Call the main function.
+if __name__ == "__main__":
+    main()
+</code>
+=====9-2=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-1. File Filtering.
+# Author: PolyMath
+#
+def main():
+    while True:
+        fname = input("Enter the name of the file here: ")
+        line_num = int(input("and the number of lines to display < 40: "))
+        try:
+            text_file = open(fname)
+            if line_num > 40:
+                continue                              # try again
+            for count in range(line_num + 1):
+                line = text_file.readline().rstrip()   # get a line of text.
+                print(line)
+        except IOError:                              # open file error.
+            print("The name of the file is 'test.txt'. try again.\n")
+            break
+    print('\nDone!')
+#
+# Call the main function.
+if __name__ == "__main__":
+    main()
+</code>
+=====9-4=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-1. File Filtering.
+# Author: PolyMath
+#
+import sys
+#
+def bye():
+    print('\nDone!')
+    sys.exit()
+#
+def main():
+    while True:
+        fname = input("\nEnter the name ('readme.txt') of the file here: ")
+        try:
+            text_file = open(fname)
+            lines = [line.rstrip() for line in text_file]   # load all the file into memory.
+            limit = len(lines)
+            char = input("Press a key to continue 'q' to quit.")
+            if char == 'q':
+                bye()
+            for line_num in range(limit):
+                print(lines[line_num])
+        except IOError:     # open file error.
+            print("The name of the file is 'readme.txt'. try again.\n")
+            bye()
+#
+# Call the main function.
+if __name__ == "__main__":
+    main()
+</code>
+=====9-5=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-5. Test Scores
+# Author: PolyMath
+#
+def get_grade(score):
+    if score > 89:
+        return 'A'
+    elif score > 79:
+        return 'B'
+    elif score > 69:
+        return 'C'
+    elif score > 69:
+        return 'D'
+    else:
+        return 'E'
+#
+def main():
+    while True:
+        reply = input("\nInput Scores data from a file y/n. ")
+        if reply == 'y':
+            fname = input("Enter the file name here: ") # get the filename
+            try:
+                fobj = open(fname, 'r') # open the file for reading.
+                line = fobj.readline()  # get the file contents.
+                line = line.rstrip()
+                scorelist = line.split(',')
+            except IOError:
+                print("\nThe filname ", fname, "does not exist.")
+                continue
+        else:
+            print('\nEnter all the scores (1 - 100) for the exam as a')
+            reply = input('comma-seperated list E.G. 65,87,34,... ')
+            if reply == '':
+                break
+            scorelist = reply.split(',')
+        # if score is a string digit, convert it to an integer and add it to scores list.
+        scores = [int(score) for score in scorelist if score.isdigit() and int(score) < 101]
+        # if the list of integers != list of strings entered, then error.
+        if len(scores) != len(scorelist):
+            print('\nTher has been an error. Try again.')
+            print("This is the list that was input:",scorelist)
+            continue
+        for score in scores:
+                print("An exam score of '{0}' is a grade '{1}'".format(score,get_grade(score)))
+        average = float(sum(scores))/len(scores)
+        print("The average score is: {0:.2f}".format(average))
+    print('Done!')
+#
+# Call the main function.
+main()
+</code>
+=====9-6=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-6. File Comparison.
+# Author: PolyMath
+#
+def main():
+    fname1 = 'readme1.txt'
+    fname2 = 'readme2.txt'
+    fobj1 = open(fname1, 'r')
+    fobj2 = open(fname2, 'r')
+    line1 = fobj1.readline()    # get the first line from the file
+    line2 = fobj2.readline()
+    line_number = 0     # initialize line count
+    while line1 == line2:
+        line1 = fobj1.readline()    # get the next line from the file
+        if not line1:
+            break
+        line2 = fobj2.readline()    # get the next line from the file
+        if not line2:
+            break
+        line_number += 1
+        col_number = 0  # initialize column count.
+    while line1[col_number] == line2[col_number]: # are the 2 lines equal.
+        col_number += 1     # yes. increment count and try again.
+    print("The two files differ on line: '{0}' and column '{1}'".format(line_number + 1, col_number + 1))
+    print("\nDone.")
+#
+# Call the main function.
+if __name__ == "__main__":
+    main()
+</code>
+=====9-13-1=====
+-13-1. Command-Line Arguments.
+"Command-line arguments are those arguments given to the program in addition
+to the script name on invocation."
+"Are command-line arguments useful? Commands on Unix-based systems are typically
+programs that take input, perform some function, and send output as a stream of
+data. These data are usually sent as input directly to the next program, which
+does some other type of function or calculation and sends the new output to
+another program, and so on. Rather than saving the output of each program and
+potentially taking up a good amount of disk space, the output is usually
+"piped" into the next program as its input."
+=====9-13-2=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-13 Command-Line Arguments.
+# Author: PolyMath
+#
+import sys
+#
+def main():
+    print("you entered the following command-line arguments: ", str(sys.argv[1:]))
+    print('\nDone!')
+#
+# Call the main function.
+if __name__ == "__main__":
+    main()
+</code>
+=====9-14=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-14.	caculator
+# Author: PolyMath
+#
+import sys
+from operator import add, sub, mul, mod,truediv, pow
+nums = [None, None]
+#
+def bye():
+    print('Done!\n')
+    sys.exit()
+#
+def main():
+    operators = {'+':add, '-':sub, '%':mod, '*':mul, '/':truediv, '^':pow}
+    expr = (sys.argv[1:])                           # get the expression
+    operator = expr[1]
+    if operator not in operators:                   # is the operator legal
+        print("Wrong operator used. use one from (+, -, *, /, %, ^)\n")
+        bye()                                       # no, then quit.
+    try:
+        nums[0] = float(expr[0])                    # are the operands numbers
+        nums[1] = float(expr[2])
+    except ValueError:                              # no, then quit
+        print("\nThere has been an error. Enter two numbers EG. '2 + 5'.")
+        bye()
+    solution = operators[operator](*nums)           # do the arithmetic
+    print("{0} {1} {2} = {3}".format(nums[0], operator, nums[1], solution))
+    bye()
+#
+# Call the main function.
+main()
+</code>
+=====9-15=====
+<code python>
+#!/usr/bin/python3
+#
+# 9-15. Copying Files.
+# Author: PolyMath
+#
+import sys
+#
+def main():
+    fname1 = sys.argv [1]
+    fname2 = sys.argv [2]
+    file1 = open(fname1, 'r')
+    file2 = open(fname2, 'w')
+    lines = file1.readlines()
+    file2.writelines(lines)
+    print("\nSucces! Copied file '{0}' to file '{1}'.".format(fname1, fname2))
+    print('\nDone!')
+#
+# Call the main function.
+if __name__ == "__main__":
+    main()
+</code>
 =====9-10=====
 ====main program====