Modes for Opening files

• We still have to open a file (open and read, or open and write)
• writing new stuff in file
  • for w and a flags, if no file is found it will create a new file
    • but for r (the default) flag if file doesn’t exist it will raise an error
• r - Read a file (default)
• w - Write to a file (Overwrite)
• a - Appends to a file
• r+ - Read AND write to a file (writing based on cursor)

Writing+appending files

w

• w flag to open()
• OVERWRITES

(story.txt)
Hello!

with open("story.txt", "w") as f:
    f.write("Hi.\n")
    f.write("Nice to meet you!\n") 

(story.txt)
Hi.
Nice to meet you!

• It gets completely overwritten!

a

• a flag to open()
• APPENDS
• You can’t use seek() because a will always move the cursor to the end

(story.txt)
Original text!

with open("story.txt", "a") as f:
	f.write("Hi.\n")
	f.write("Nice to meet you!\n")

(story.txt)
Original text!
Hi.
Nice to meet you!

r+

• super common
• doesn’t create a new file tho → the idea is that it “updates” an existing file

(story.txt)
I WAS HERE FIRST!

with open("story.txt", "r+") as f:
    f.write("Added using r+")

(story.txt)
Added using r+ST!

• The initial write (f.write("Testing..\n")) writes "Testing..\n" at the beginning of the file.
• Then, f.write("This is a test!") writes over the beginning of the file again, overwriting the characters that were written by the first write.

Exercises

"""==========================================================="""
""" Copying content of file to file 2"""
def copy(file, file2):
    with open(file) as f:
        content = f.read()
    
    with open(file2, 'w') as f2:
        f2.write(content)
 
# other ppl's approaches (wtf)
def copy(file1, file2):
    with open(file1) as f1, open(file2, "w") as f2: 
	    f2.write(f1.read())
 
"""==========================================================="""
"""Copy and reverse content of file 1 to file2"""
def copy_and_reverse(file1, file2):
    with open(file1) as f1, open(file2, 'w') as f2:
        reverse = f1.read()[::-1]
        f2.write(reverse)
 
#other ppl's approaches (wtf22)
def copy_and_reverse(file1, file2):
    with open(file1) as f1, open(file2, "w") as f2:
		    f2.write(''.join(reversed(f1.read())))
 
"""==========================================================="""
"""returns dict with # of lines, words, and chars in the file"""
def statistics(file):
    ans = {}
    with open(file) as f:
        ans['lines'] = len(f.readlines())
        f.seek(0)
        ans['words'] = len(f.read().split())
        f.seek(0)
        ans['characters'] = len(f.read())
    
    return ans
 
# (wtf?)
def statistics(f):
    return {"lines": len(open(f).readlines()), "words":
	    len(open(f).read().split()), "characters": len(open(f).read())}
# official solution
    def statistics(file_name):
        with open(file_name) as file:
            lines = file.readlines()
     
        return { "lines": len(lines),
                 "words": sum(len(line.split(" ")) for line in lines),
                 "characters": sum(len(line) for line in lines) }
                 
"""==========================================================="""
"""Write a function called find_and_replace, which takes in a file name, a word to search for, and a replacement word"""
def find_and_replace(file, word1, word2):
    with open(file, 'r+') as f: # read AND write
        text = f.read()
        new_text = text.replace(word1, word2)
        
	    f.seek(0)
        f.write(new_text)
        f.truncate() 
        # removes/trim the leftovers
		# if len(word2) < len(word1) then the entire text gets shorter, so we
		# get rid of the leftovers
```