Add files via upload

Author: Jian-Chueng

Chapter 07: Files/ch07_file.py

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+# 1.file hande as a sequence
+handle = open('test.txt')
+for cheese in handle:
+    print(cheese)
+# cheese means iteration variable, print out each line of file test.txt
+print('#####################################################')
+# 2.counting lines in a file
+handle = open('test.txt')
+count = 0
+for line in handle:
+    count = count+1
+print('Line count:', count)
+# 2.counting lines in a file
+handle = open('mbox.txt')
+count = 0
+for line in handle:
+    count = count+1
+print('Line count:', count)
+# "line" is just a random name of iteration variable!
+print('#####################################################')
+print('3.Reading the *whole* file')
+print('you can red the whole file (newline and all) '
+      'into a single string')
+fhand = open('test.txt')
+ghand = open('test.txt', 'r')
+# you have to use string.read() to read whole thing into string,
+# also read newline as "\n"
+inp = fhand.read()
+print(len(inp))  # print the length of the file
+print(inp)
+print('fhand is', fhand)
+print('ghand is', ghand)
+# means 'r' in open doesn't read the file
+print(inp[:20])  # print out the first 20 letters
+# (not included the 20th character!)
+print('#####################################################')
+# 4.Search through a file
+print('put an "if" statement in "for" loop '
+      'to only print out certain lines')
+fhand = open('mbox_short.txt')
+for line in fhand:
+    if line.startswith('From: '):
+        print(line)
+# already checked, all lines meet the criteria are printed out
+# Problem: lots of blank line between each line.
+# Reason: 1. each line from the file has a "newline" at the end
+#         2. "print" statement add "newline" to each line
+#Solution: strip the whitespace from
+# the right-hand side of the string using "rstrip()"
+# newline is considered as whitespace
+print('fixed version: strip newline:')
+fhand = open('mbox_short.txt')
+for line in fhand:
+    if line.startswith('From: '):
+        print(line.rstrip())
+# or print('fixed version: strip newline:')
+# fhand = open('mbox_short.txt')
+# for line in fhand:
+#     line = line.rstrip() <---------------------
+#     if line.startswith('From: '):
+#         print(line)
+print('#####################################################')
+print('4.skipping with continue')
+print('we can conveniently skip a line by '
+      'using "continue" statement')
+fhand = open('test.txt')
+for line in fhand:
+    line = line.rstrip()
+    if line.startswith('From: '):
+        continue
+    print(line)
+print('*******************')
+fhand = open('test.txt')
+for line in fhand:
+    line = line.rstrip()
+    # Skip 'uninteresting lines'
+    if not line.startswith('From:'):
+        continue
+    # Process our 'interesting' line
+    print(line)
+print('#####################################################')
+print('5. Usnig "in" to select lines')
+print('we can find a string in a line as our selection criteria')
+fhand = open('test.txt')
+for line in fhand:
+    line = line.rstrip()
+    if not '@uct.ac.za' in line:
+        continue
+    print(line)
+print('**********************')
+fhand = open('test.txt')
+for line in fhand:
+    line = line.rstrip()
+    if line.find('@uct.ac.za')== -1:
+        continue
+    print(line)
+    print(line.find('@uct.ac.za'))
+    #'find' statement:  either returns the position of the string
+    #  or -1 if the string was not found
+print('#####################################################')
+print('6.promp with file name')
+fname = input('Enter the file name: ')
+try:
+    fhand = open(fname)
+except:
+    print('File cannot be opened:', fname)
+    exit()
+subject = input('we gonna find: ')
+count =0
+for line in fhand:
+    line = line.rstrip()
+    if line.startswith(subject):
+        count = count+1
+print('there are', count, 'subject lines in', fname )
+print('#####################################################')

Chapter 07: Files/ch07_hw1.py

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+print('Exercise 1: Write a program to read through a file and '
+      'print the contents of the file (line by line) all in upper case.')
+fname = open ('mbox.txt')
+for line in fname:
+    line = line.rstrip()
+    print(line.upper())

Chapter 07: Files/ch07_hw2.py

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+
+# Use the file name mbox-short.txt as the file name
+fname = input("Enter file name: ")
+fh = open(fname)
+sum = 0.0
+count = 0
+
+for line in fh:
+    line = line.rstrip()
+    if not line.startswith("X-DSPAM-Confidence:"):
+        continue
+    sum = sum + float(line[20:])
+    count = count + 1
+
+print("Average spam confidence:", sum/count)

Chapter 07: Files/ch07_quiz

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+Question 1
+Given the architecture and terminology we introduced in Chapter 1, where are files stored?
+Motherboard
+Central Processor
+Machine Language
+Secondary memory
+
+Answer: Secondary memory
+
+Question 2
+What is stored in a "file handle" that is returned from a successful open() call?
+The handle has a list of all of the files in a particular folder on the hard drive
+The handle is a connection to the file's data
+The handle contains the first 10 lines of a file
+All the data from the file is read into memory and stored in the handle
+
+Answer: The handle is a connection to the file's data
+
+Question 3
+What do we use the second parameter of the open() call to indicate?
+How large we expect the file to be
+The list of folders to be searched to find the file we want to open
+Whether we want to read data from the file or write data to the file
+What disk drive the file is stored on
+
+Question 4
+What Python function would you use if you wanted to prompt the user for a file name to open?
+file_input()
+read()
+raw_input()
+cin
+
+Answer: raw_input()
+
+Question 5
+What is the purpose of the newline character in text files?
+It adds a new network connection to retrieve files from the network
+It indicates the end of one line of text and the beginning of another line of text
+It enables random movement throughout the file
+It allows us to open more than one files and read them in a synchronized manner
+
+Answer: It indicates the end of one line of text and the beginning of another line of text
+
+Question 6
+If we open a file as follows:
+xfile = open('mbox.txt')
+What statement would we use to read the file one line at a time?
+
+for line in xfile:
+while ( getline (xfile,line) ) {
+READ xfile INTO LINE
+READ (xfile,*,END=10) line
+                
+Answer: for line in xfile
+
+Question 7
+What is the purpose of the following Python code?
+fhand = open('mbox.txt')
+x = 0
+for line in fhand:
+        x = x + 1
+print x
+Count the lines in the file 'mbox.txt'
+Reverse the order of the lines in mbox.txt
+Remove the leading and trailing spaces from each line in mbox.txt
+Convert the lines in mbox.txt to upper case
+
+Answer: Count the lines in the file 'mbox.txt'
+
+Question 8
+If you write a Python program to read a text file and you see extra blank lines in the output that are not present in the file input as shown below, what Python string function will likely solve the problem?
+From: [email protected]
+
+From: [email protected]
+
+From: [email protected]
+
+From: [email protected]
+...
+find()
+startswith()
+rstrip()
+split()
+Answer: rstrip()
+
+Question 9
+The following code sequence fails with a traceback when the user enters a file that does not exist. How would you avoid the traceback and make it so you could print out your own error message when a bad file name was entered?
+fname = raw_input('Enter the file name: ')
+fhand = open(fname)
+try / except
+signal handlers
+try / catch / finally
+on error resume next
+
+Answer: try/ except
+
+Question 10
+What does the following Python code do?
+fhand = open('mbox-short.txt')
+inp = fhand.read()
+Checks to see if the file exists and can be written
+Turns the text in the file into a graphic image like a PNG or JPG
+Reads the entire file into the variable inp as a string
+Prompts the user for a file name
+
+Answer: Reads the entire file into the variable inp as a string