# Zhi Yuan "Oscar" Lin # 8 November 2021 # In this lesson, I learned how to use the file methods, ".write()" and ".seek()" through examples and tasks. Additionally, # I learned when to use the a+, w+, and r+ modes. As for the rest, it was review which included the following: importing, # opening, and closing a file, using the ".strip()" method, and using file method ".write()". # There were no major problems or questions throughout this lesson.

# [ ] review and run example # - creates a new local file or overwrites the local file (makes it blank) # The variable "new_file" is assigned to the return file object from using the open() function to open the file named # "new_file.txt" in write mode, and text mode by default. new_file = open('new_file.txt', 'w')

# [ ] review and run example to write some text to the file # This line of code writes the text "This is line #1 with 'w'\nThis is line #2 with 'w'\nThis is line #3 withn 'w'!\n" to # the new_file file, by using the file method ".write()". new_file.write("This is line #1 with 'w'\nThis is line #2 with 'w'\nThis is line #3 withn 'w'!\n")

# [ ] review and run example # - close file and re-open in read mode # - head pointer is at start of file # This line of code removes the reference created by the file open() function that is assigned to the new_file variable, by # using the file method ".close()". new_file.close() # The variable "new_file" is assigned to the return file object from using the open() function to open the file named # "new_file.txt" in read mode, and text mode by default. new_file = open('new_file.txt', 'r')

# [ ] review and run example to see what was written to the file # The variable "new_text" is assigned to the given value when the file "new_file" is attached to the file method ".read()". new_text = new_file.read() # This function displays the value assigned to the new_text variable in the output. print(new_text) # This line of code removes the reference created by the file open() function that is assigned to the new_file variable, by # using the file method ".close()". new_file.close()

# [ ] open planets.txt in write mode # The variable "inner_planets_file" is assigned to the return file object from using the open() function to open the file # named "inner_planets.txt" in write mode, and text mode by default. inner_planets_file = open('inner_planets.txt', 'w')

# [ ] write Mercury, Venus, Earth, Mars on separate lines # This line of code writes the text "Mercury\nVenus\nEarth\nMars\n" to the inner_planets_file file, by using the file method # ".write()". inner_planets_file.write('Mercury\nVenus\nEarth\nMars\n')

# [ ] close the file and re-open in read mode # This line of code removes the reference created by the file open() function that is assigned to the inner_planets_file # variable, by using the file method ".close()". inner_planets_file.close() # The variable "inner_planets_file" is assigned to the return file object from using the open() function to open the file # named "inner_planets.txt" in read mode, and text mode by default. inner_planets_file = open('planets.txt', 'r')

# [ ] use .read() to read the entire file contents # The variable "inner_planets_text" is assigned to the given value when the file "planets_file" is attached to the file # method ".read()". inner_planets_text = inner_planets_file.read()

# [ ] print the entire file contents and close the file # This function displays the value assigned to the inner_planets_text variable in the output. print(inner_planets_text) # This line of code removes the reference created by the file open() function that is assigned to the inner_planets_file # variable, by using the file method ".close()". inner_planets_file.close()

# [ ] review and run example # creates a new local file or overwrites the local file (makes it blank) # The variable "new_file" is assigned to the return file object from using the open() function to open the file named # "new_file.txt" in write and read mode (overwrites), and text mode by default. new_file = open('new_file.txt', 'w+')

# [ ] review and run example to see what was written to the file # - 'w+' overwrites, we can read, but the file is ***BLANK*** # The variable "new_text" is assigned to the given value when the file "new_file" is attached to the file method ".read()". new_text = new_file.read() # This function displays the value assigned to the new_text variable in the output. print(new_text)

# [ ] review and run - write to the blank file # This line of code writes the text "This is line #1 with 'w+'\nThis is line #2 with 'w+'\n" to the new_file file, by using # the file method ".write()". new_file.write("This is line #1 with 'w+'\nThis is line #2 with 'w+'\n")

# [ ] review and run example - read and print (Note: the pointer is at the end of the file - result = empty string) # The variable "new_text" is assigned to the given value when the file "new_file" is attached to the file method ".read()". new_text = new_file.read() # This function displays the value assigned to the new_text variable in the output. print(new_text)

# [ ] review and run example - sets pointer to beginning of file # This line of code sets the pointer to the beginning of the file assigned to the new_file variable due to the file method # ".seek()". new_file.seek(0)

# [ ] review and run example - now read starts from beginning of file # The variable "new_text" is assigned to the given value when the file "new_file" is attached to the file method ".read()". new_text = new_file.read() # This function displays the value assigned to the new_text variable in the output. print(new_text)

# # [ ] review and run example - clean up and close file # This line of code removes the reference created by the file open() function that is assigned to the new_file variable, by # using the file method ".close()". new_file.close()

# [ ] open outer_planets.txt in write mode 'w+' # The variable "outer_planets_file" is assigned to the return file object from using the open() function to open the file # named "outer_planets.txt" in write and read mode (overwrites), and text mode by default. outer_planets_file = open('outer_planets.txt', 'w+')

# [ ] write four outer planets in earth's solar system (Jupiter, Saturn, Uranus, Neptune) on separate lines # This line of code writes the text "Jupiter\nSaturn\nUranus\nNeptune\n" to the outer_planets_file file, by using the file # method ".write()". outer_planets_file.write("Jupiter\nSaturn\nUranus\nNeptune\n")

# [ ] use .seek() to move the pointer to the start of the file # [ ] use .read() to read the entire file contents # This line of code sets the pointer to the beginning of the file assigned to the outer_planets_file variable due to the # file method ".seek()". outer_planets_file.seek(0) # The variable "outer_planets_text" is assigned to the given value when the file "outer_planets_file" is attached to the # file method ".read()". outer_planets_text = outer_planets_file.read()

# [ ] print the entire file contents and close the file # This function displays the value assigned to the outer_planets_text in the output. print(outer_planets_text) # This line of code removes the reference created by the file open() function that is assigned to the outer_planets_file # variable, by using the file method ".close()". outer_planets_file.close()

# [ ] review and run - create, write, read and print a file # The variable "tips_file" is assigned to the return file object from using the open() function to open the file named # "code_tips.txt" in write and read mode (overwrites), and text mode by default. tips_file = open('code_tips.txt', 'w+') # This line of code writes the text "-use simple function and variable names\n-comment code\n-organize code into functions\n" # to the tips_file file, by using the file method ".write()". tips_file.write('-use simple function and variable names\n-comment code\n-organize code into functions\n') # This line of code sets the pointer to the beginning of the file assigned to the tips_file variable due to the file method # ".seek()". tips_file.seek(0) # The variable "tips_text" is assigned to the given value when the file "tips_file" is attached to the file method ".read()". tips_text = tips_file.read() # This function displays the value assigned to the tips_text variable. print(tips_text)

# [ ] review and run example - setting a specific seek() index # This line of code sets the pointer to the start of the 14th character of the file assigned to the tips_file variable due # to the file method ".seek()". tips_file.seek(13) # now read starts from 14th character of file # The variable "tips_text" is assigned to the given value when the file "tips_file" is attached to the file method ".read()". tips_text = tips_file.read() # This function displays the value assigned to the tips_text variable. print(tips_text)

# [ ] review and run example - string slicing on a read of an entire file # read from the start # This line of code sets the pointer to the beginning of the file assigned to the tips_file variable due to the file method # ".seek()". tips_file.seek(0) # The variable "tips_text" is assigned to the given value when the file "tips_file" is attached to the file method ".read()". tips_text = tips_file.read() # slice from the 14th character to end # This function only displays the 14th to the last character of the value assigned to the tips_text variable in the output. print(tips_text[13:])

# [ ] review and run example - setting pointer to end of file with whence value = 2 # This line of code sets the pointer to the end of the file assigned to the tips_file variable due to the file method # ".seek()". tips_file.seek(0,2) # This line of code adds the text "-use seek(0,2) to set read/write at end of file\n" to the tips_file file, by using the # file method ".write()". tips_file.write("-use seek(0,2) to set read/write at end of file\n") # read from beginning of file - .seek(0,0) is same as .seek(0) # This line of code sets the pointer to the beginning of the file assigned to the tips_file variable due to the file method # ".seek()". tips_file.seek(0,0) # The variable "tips_text" is assigned to the given value when the file "tips_file" is attached to the file method ".read()". tips_text = tips_file.read() # This function displays the value assigned to the tips_text variable in the output. print(tips_text)

# [ ] review and run example - point to file beginning and overwrite 1st line # This line of code sets the pointer to the beginning of the file assigned to the tips_file variable due to the file method # ".seek()". tips_file.seek(0) # This line of code replaces the 1st line of the tips_file variable with the text "'-use simple function and variable #names\n', by using the file method ".write()", after it is changed into all uppercases due to the string method ".upper()". tips_file.write('-use simple function and variable names\n'.upper())

# [ ] review and run example - show new file contents # This line of code sets the pointer to the beginning of the file assigned to the tips_file variable due to the file method # ".seek()". tips_file.seek(0,0) # The variable "tips_text" is assigned to the given value when the file "tips_file" is attached to the file method ".read()". tips_text = tips_file.read() # This function displays the value assigned to the tips_text variable in the output. print(tips_text)

# [ ] open a new file days.txt in write plus read mode 'w+' # [ ] write week days (Monday - Friday) on separate lines to the file # The variable "days_file" is assigned to the return file object from using the open() function to open the file named # "days.txt" in write and read mode (overwrites), and text mode by default. days_file = open('days.txt', "w+") # This line of code writes the text "Monday\nTuesday\nWednesday\nThursday\nFriday\n" to the days_file file, by using the # file method ".write()". days_file.write("Monday\nTuesday\nWednesday\nThursday\nFriday\n")

# [ ] use .seek() to move the pointer to the start of the file # [ ] use .read() to read the entire file contents # [ ] print the entire file contents and close the file # This line of code sets the pointer to the beginning of the file assigned to the tips_file variable due to the file method # ".seek()". days_file.seek(0) # The variable "days_text" is assigned to the given value when the file "days_file" is attached to the file method ".read()". days_text = days_file.read() # This function displays the value assigned to the days_text variable in the output. print(days_text)

# [ ] use .seek() to move the pointer to the end of the file # [ ] write the weekend days (Saturday & Sunday) # This line of code sets the pointer to the end of the file assigned to the days_file variable due to the file method # ".seek()". days_file.seek(0,2) # This line of code adds the text "Saturday\nSunday\n" to the tips_file file, by using the file method ".write()". days_file.write("Saturday\nSunday\n")

# [ ] use .seek() to move the pointer to the start of the file # [ ] use .read() to read the entire file contents # [ ] print the entire file contents and close the file # This line of code sets the pointer to the beginning of the file assigned to the days_file variable due to the file method # ".seek()". days_file.seek(0) # The variable "days_text" is assigned to the given value when the file "days_file" is attached to the file method ".read()". days_text = days_file.read() # This function displays the value assigned to the days_text variable in the output. print(days_text)

# [ ] review and run example - function writes to the open log argument # loads funtion into memory but the funtion is not called # This program defines a function named "logger", that contains the parameter "log", with the variable "log_entry" that will # be assigned to the entry the user inputs when presented with the string "enter log item (enter to quit): ". Subsequently, # the count variable is assigned to the integer "0". Additionally, there is a while loop. In this case, the while loop is # followed by the variable "log_entry". Hence, it will evaluate true as long there there is a value assigned to the # log_entry variable. Additionally, the codes that are indented and follow the while loop will be part of the loop. Thus, # the loop starts with the count variable being reassigned to the value assigned to the count variable incremented by the # integer "1". Subsequently, the text, formed from the value assigned to the count varibale, after it is changed into a # string due to the str() function, the string ": ", the value assigned to the log_entry variable, and the escape character # "\n", to the log file, by using the file method ".write()". Following that, the log_entry variable will be reassigned to # the entry the user inputs when presented with the string "enter log item (enter to quit): ". The loop will continue until # while loop evaluates false. Subsequently, when the while loop ends, the value assigned to the count variable will be # return due to the keyword "return". def logger(log): log_entry = input("enter log item (enter to quit): ") count = 0 while log_entry: count += 1 log.write(str(count) + ": " + log_entry + "\n") log_entry = input("enter log item (enter to quit): ") return count

# [ ] review and run example: makes a blank file (initialize/reset) # The variable "log_file" is assigned to the return file object from using the open() function to open the file named # "code_tips.txt" in write and read mode (overwrites), and text mode by default. log_file = open('log_file.txt', 'w+') # This line of code removes the reference created by the file open() function that is assigned to the log_file variable, by # using the file method ".close()". log_file.close()

# [ ] review and run example - opens the log_file before passing to logger() function call, below # allows for calls below to run several times appending to the end of log_file # The variable "log_file" is assigned to the return file object from using the open() function to open the file named # "code_tips.txt" for appending to end of the file and in read mode (no overwrite), and text mode by default. log_file = open('log_file.txt', 'a+')

# [ ] review and run example - calls the above logger() function # what happens running the cell above (a+) again before running this cell again? # what happens if log_file.seek(0) is run before an append? # This code calls the logger() function with the argument "log_file", which is a variable, and displays the returned value # in the output. logger(log_file) # This line of code sets the pointer to the beginning of the file assigned to the log_file variable due to the file method # ".seek()". log_file.seek(0) # The variable "log_text" is assigned to the given value when the file "log_file" is attached to the file method ".read()". log_text = log_file.read() # This function displays a blank line in the output due to it not containing an argument. print() # This variable displays the value assigned to the log_text variable in the output. print(log_text) # This line of code removes the reference created by the file open() function that is assigned to the log_file variable, by # using the file method ".close()". log_file.close()

# [ ] review and run example - create a file with initial count of 0 # The variable "count_file" is assigned to the return file object from using the open() function to open the file named # "count_file.txt" in write and read mode (overwrites), and text mode by default. count_file = open("count_file.txt", "w+") # This line of code adds the text "Count is: 0" to the count_file file, by using the file method ".write()". count_file.write("Count is: 0") # This line of code sets the pointer to the beginning of the file assigned to the count_file variable due to the file method # ".seek()". count_file.seek(0) # This function displays the string form of the first line of the value assigned to the count_file variable due to the file # method ".readline()", after the leading and trailing whitespace in the value assigned to the count_file variable are # removed due to it being attached to the .strip() method, in the output. print(count_file.readline().strip()) # This line of code removes the reference created by the file open() function that is assigned to the count_file variable, # by using the file method ".close()". count_file.close()

# [ ] review and run example - can rerun this cell # The variable "count_file" is assigned to the return file object from using the open() function to open the file named # "count_file.txt" in read and write mode (no overwrite), and text mode by default. count_file = open("count_file.txt", "r+") # This line of code sets the pointer to the beginning of the file assigned to the count_file variable due to the file method # ".seek()". count_file.seek(0) # The variable "count_line" is assigned to the string form of the first line of the value assigned to the count_file # variable due to the file method ".readline()", after the leading and trailing whitespace in the value assigned to the # count_file variable are removed due to it being attached to the .strip() method. count_line = count_file.readline().strip() # This variable displays the string "BEFORE", a newline due to the escape character "\n", and the value assigned to the # count_line variable in the output. print("BEFORE\n" + count_line) # get the int character(s) after the colon and space, cast and increment # The variable "count" is assigned to the value given when the 11th character (no other characters after that) is converted # into an integer, due to the int() function, incremented by the integer "1". count = int(count_line[10:])+1 # write the incremented value to the file - overwrite before value # This line of code sets the pointer to the start of 11th character of the file assigned to the count_file variable due to # the file method ".seek()". count_file.seek(10) # This line of code adds the text value assigned to the count variable, after it is changed into a string due to the str() # function, to the count_file file, by using the file method ".write()". count_file.write(str(count)) # This line of code sets the pointer to the beginning of the file assigned to the count_file variable due to the file method # ".seek()". count_file.seek(0) # This function displays a newline due to the escape character "\n", the string "AFTER", a newline due to the escape # character "\n", and the string form of the first line of the value assigned to the count_file variable due to the file # method ".readline()", after the leading and trailing whitespace in the value assigned to the count_file variable are # removed due to it being attached to the .strip() method, in the output. print("\nAFTER\n" + count_file.readline().strip()) # This line of code removes the reference created by the file open() function that is assigned to the count_file variable, # by using the file method ".close()". count_file.close()

# [ ] review funtion code for inc_count() funtion that reads file and updates the count # the file always has 1 line that is The count is: N, where N is an integer # This program defines a function named "inc_count", that contains the parameter "cnt_file", with a line of code that sets # the pointer to the beginning of the file assigned to the cnt_file variable due to the file method ".seek()". Additionally, # the cnt_line variable is assigned the string form of the first line of the value assigned to the cnt_file variable due to # the file method ".readline()", after the leading and trailing whitespace in the value assigned to the cnt_file variable # are removed due to it being attached to the .strip() method. Subsequently, the cnt variable is assigned to the value given # when the 11th character (no other characters after that) is converted into an integer, due to the int() function, # incremented by the integer "1". Following that, there is a line of code that sets the pointer to the 11th character of the # file assigned to the count_file variable due to the file method ".seek()". Additionally, there is a line of code that adds # the text value assigned to the cnt variable, after it is changed into a string due to the str() function, to the cnt_file # file, by using the file method ".write()". Subsequently, the value assigned to the cnt variable will be return due to the # keyword "return". def inc_count(cnt_file): cnt_file.seek(0,0) cnt_line = cnt_file.readline().strip() cnt = int(cnt_line[10:])+1 cnt_file.seek(10,0) cnt_file.write(str(cnt)) return cnt

# [ ] review and run example with call to function: inc_count() - **Run cell multiple times** # opens file/prints initial value # The variable "count_file" is assigned to the return file object from using the open() function to open the file named # "count_file.txt" in read and write mode (no overwrite), and text mode by default. count_file = open("count_file.txt", "r+") # This line of code sets the pointer to the beginning of the file assigned to the count_file variable due to the file method # ".seek()". count_file.seek(0) # The variable "count_line" is assigned to the string form of the first line of the value assigned to the count_file # variable due to the file method ".readline()", after the leading and trailing whitespace in the value assigned to the # count_file variable are removed due to it being attached to the .strip() method. count_line = count_file.readline().strip() # This variable displays the string "BEFORE", a newline due to the escape character "\n", and the value assigned to the # count_line variable in the output. print("BEFORE\n" + count_line) # call inc_count() to increase the count 5 times # By using the for...in loop, a sequence of integers generated by the range() function (with a start value of 0, a stop # value of 5, and a step value of 1), is iterated. Additionally, the count variable is assigned to the returned value when # calling the inc_count() function with the arguement "count_file", that is variable. Subsequently, there is a line of code # that will set the pointer to the beginning of the file assigned to the count_file variable due to the file method # ".seek()". Following that, a newline due to the escape character "\n", the string "AFTER inc_count() call", the value # given wehn the value assigned to the i variable is incremented by the integer "1". a newline due to the escape character # "\n", and the string form of the first line of the value assigned to the count_file variable due to the file method # ".readline()", after the leading and trailing whitespace in the value assigned to the count_file variable are removed due # to it being attached to the .strip() method, in the output. This loop will continue until each element generated by the # range() function is iterated. for i in range(5): count = inc_count(count_file) count_file.seek(0) print("\nAFTER inc_count() call", i+1, "\n" + count_file.readline().strip()) # This line of code removes the reference created by the file open() function that is assigned to the count_file variable, # by using the file method ".close()". count_file.close()

# [ ] complete the task # The variable "task4_file" is assigned to the return file object from using the open() function to open the file named # "task4_file.txt" in write and read mode (overwrites), and text mode by default. task4_file = open('task4_file.txt', 'w+') # This line of code writes the text "Line1\nLine2\nLine3\n" to the task4_file file, by using the file method ".write()". task4_file.write("Line1\nLine2\nLine3\n") # This line of code removes the reference created by the file open() function that is assigned to the task4_file variable, # by using the file method ".close()". task4_file.close() # [ ] code here # The variable "task4_file" is assigned to the return file object from using the open() function to open the file named # "task4_file.txt" for appending to end of the file and in read mode (no overwrite), and text mode by default. task4_file = open('task4_file.txt', 'a+') # By using the for...in loop, a sequence of integers generated by the range() function (with a start value of 0, a stop # value of 5, and a step value of 1), is iterated. Additionally, there is a line of code that adds the text, with the string # "append #", the value assigned to the item variable after it is changed into a string due to the str() function, and a # newline due to the escape character "\n", to the task4_file file, by using the file method ".write()". Additionally, there # is a line of code that sets the pointer to the beginning of the file assigned to the task4_file variable, due to the file # method ".seek()". This loop will continue until each element generated by the range() function is iterated. for item in range(5): task4_file.write("append #" + str(item) +"\n") task4_file.seek(0) # This function displays the given value when attaching the task4_file variable to the file method ".read()", in the output. print(task4_file.read()) # This line of code removes the reference created by the file open() function that is assigned to the task4_file variable, # by using the file method ".close()". task4_file.close()

# [ ] complete the task # The variable "task5_file" is assigned to the return file object from using the open() function to open the file named # "task5_file.txt" in write and read mode (overwrites), and text mode by default. task5_file = open('task5_file.txt', 'w+') # This line of code writes the text "Line\nLine2\nLine3\nLine4\nLine5\nLine6\nLine7\nLine8\nLine9\nLine10\n" to the # task5_file file, by using the file method ".write()". task5_file.write("Line\nLine2\nLine3\nLine4\nLine5\nLine6\nLine7\nLine8\nLine9\nLine10\n") # This line of code that sets the pointer to the beginning of the file assigned to the task5_file variable, due to the file # method ".seek()". task5_file.seek(0) # This function displays the given value by attaching the task5_file varibale to the file method ".read()", and a newline, # due to the escape character "\n", in the output. print(task5_file.read(),"\n") # This line of code removes the reference created by the file open() function that is assigned to the task5_file variable, # by using the file method ".close()". task5_file.close() # [ ] code here # The variable "task5_file" is assigned to the return file object from using the open() function to open the file named # "task5_file.txt" in read and write mode (no overwrite), and text mode by default. task5_file = open('task5_file.txt', 'r+') # By using the for...in loop, a sequence of integers generated by the range() function (with a start value of 0, a stop # value of 6, and a step value of 1), is iterated. Additionally, there is a line of code that adds the text, with the string # "write (r+) #", the value assigned to the item variable after it is changed into a string due to the str() function, and # a newline due to the escape character "\n", to the task5_file file, by using the file method ".write()". Additionally, # there is a line of code that sets the pointer in the position given from the value of item variable times the integer "11", # of the file assigned to the task5_file variable, due to the file method ".seek()". This loop will continue until each # element generated by the range() function is iterated. for item in range(1,6): task5_file.write("write (r+) #" + str(item)+ "\n") task5_file.seek(item*11) # This function displays the given value when attaching the task5_file variable to the file method ".read()", in the output. print(task5_file.read()) # This line of code removes the reference created by the file open() function that is assigned to the task5_file variable, # by using the file method ".close()". task5_file.close()