# Charles Edgar # November 8, 2021 # In this lesson I learned how to write in a file and how to use .seek() to set a read or write location. # In this lesson I had trouble understanding the 'r+' mode, especially with loops. It was hard for me to find mistakes when I could # only see the output of the program and not the processes it took to get there. Trying to understand what was happening and when it # was happening was difficult. To get a better understanding, I temporarily used a print statement within the loop so that I could # see step by step what was happening so that I could have a clear picture in my head of what I needed to do.

# [ ] review and run example # - creates a new local file or overwrites the local file (makes it blank) new_file = open('new_file.txt', 'w')

# [ ] review and run example to write some text to the file 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 new_file.close() new_file = open('new_file.txt', 'r')

# [ ] review and run example to see what was written to the file new_text = new_file.read() print(new_text) new_file.close()

# [ ] open planets.txt in write mode planets = open('inner_planets.txt','w')

# [ ] write Mercury, Venus, Earth, Mars on separate lines planets.write('Mercury\nVenus\nEarth\nMars')

# [ ] close the file and re-open in read mode planets.close() planets = open('inner_planets.txt','r')

# [ ] use .read() to read the entire file contents planet_text = planets.read()

# [ ] print the entire file contents and close the file print(planet_text) planets.close()

# [ ] review and run example # creates a new local file or overwrites the local file (makes it blank) 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*** new_text = new_file.read() print(new_text)

# [ ] review and run - write to the blank file 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) new_text = new_file.read() print(new_text)

# [ ] review and run example - sets pointer to beginning of file new_file.seek(0)

# [ ] review and run example - now read starts from beginning of file new_text = new_file.read() print(new_text)

# # [ ] review and run example - clean up and close file new_file.close()

# [ ] open outer_planets.txt in write mode 'w+' planets = open('outer_planets.txt','w+')

# [ ] write four outer planets in earth's solar system (Jupiter, Saturn, Uranus, Neptune) on separate lines planets.write('Jupiter\nSaturn\nUranus\nNeptune')

# [ ] use .seek() to move the pointer to the start of the file planets.seek(0) # [ ] use .read() to read the entire file contents planets_text = planets.read()

# [ ] print the entire file contents and close the file print(planets_text) planets.close()

# [ ] review and run - create, write, read and print a file tips_file = open('code_tips.txt', 'w+') tips_file.write('-use simple function and variable names\n-comment code\n-organize code into functions\n') tips_file.seek(0) tips_text = tips_file.read() print(tips_text)

# [ ] review and run example - setting a specific seek() index tips_file.seek(13) # now read starts from 14th character of file tips_text = tips_file.read() print(tips_text)

# [ ] review and run example - string slicing on a read of an entire file # read from the start tips_file.seek(0) tips_text = tips_file.read() # slice from the 14th character to end print(tips_text[13:])

# [ ] review and run example - setting pointer to end of file with whence value = 2 tips_file.seek(0,2) 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) tips_file.seek(0,0) tips_text = tips_file.read() print(tips_text)

# [ ] review and run example - point to file beginning and overwrite 1st line tips_file.seek(0) tips_file.write('-use simple function and variable names\n'.upper())

# [ ] review and run example - show new file contents tips_file.seek(0,0) tips_text = tips_file.read() print(tips_text)

# [ ] open a new file days.txt in write plus read mode 'w+' days = open('days.txt','w+') # [ ] write week days (Monday - Friday) on separate lines to the file days.write('Monday\nTuesday\nWednesday\nThursday\nFriday\n')

# [ ] use .seek() to move the pointer to the start of the file days.seek(0) # [ ] use .read() to read the entire file contents days_text = days.read() # [ ] print the entire file contents and close the file print(days_text)

# [ ] use .seek() to move the pointer to the end of the file days.seek(0,2) # [ ] write the weekend days (Saturday & Sunday) days.write('Saturday\nSunday\n')

# [ ] use .seek() to move the pointer to the start of the file days.seek(0) # [ ] use .read() to read the entire file contents days_text = days.read() # [ ] print the entire file contents and close the file print(days_text)

# [ ] review and run example - function writes to the open log argument # loads funtion into memory but the funtion is not called 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) log_file = open('log_file.txt', 'w+') 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 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? logger(log_file) log_file.seek(0) log_text = log_file.read() print() print(log_text) log_file.close()

# [ ] review and run example - create a file with initial count of 0 count_file = open("count_file.txt", "w+") count_file.write("Count is: 0") count_file.seek(0) print(count_file.readline().strip()) count_file.close()

# [ ] review and run example - can rerun this cell count_file = open("count_file.txt", "r+") count_file.seek(0) count_line = count_file.readline().strip() print("BEFORE\n" + count_line) # get the int character(s) after the colon and space, cast and increment count = int(count_line[10:])+1 # write the incremented value to the file - overwrite before value count_file.seek(10) count_file.write(str(count)) count_file.seek(0) print("\nAFTER\n" + count_file.readline().strip()) 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 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 count_file = open("count_file.txt", "r+") count_file.seek(0) count_line = count_file.readline().strip() print("BEFORE\n" + count_line) # call inc_count() to increase the count 5 times 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()) count_file.close()

# [ ] complete the task task4_file = open('task4_file.txt', 'w+') task4_file.write("Line1\nLine2\nLine3\n") task4_file.close() # [ ] code here # Opens file in append plus mode task4_file = open('task4_file.txt','a+') # Writes to end of file five times for item in range(5): task4_file.write('append #' + str(item) + '\n') task4_file.seek(0) # Prints file contents task4_text = task4_file.read() print(task4_text)

# [ ] complete the task task5_file = open('task5_file.txt', 'w+') task5_file.write("Line\nLine2\nLine3\nLine4\nLine5\nLine6\nLine7\nLine8\nLine9\nLine10\n") task5_file.seek(0) print(task5_file.read(),"\n") task5_file.close() # [ ] code here # Opens file in read plus mode task5_file = open('task5_file.txt','r+') task5_file.seek(0) # Writes to the file and sets a new write location. Repeats five times for item in range(1,6): task5_file.write('write (r+) #' + str(item)+'\n') task5_file.seek(item*11) # Prints file contents task5_file.seek(0) task5_text = task5_file.read() print(task5_text)