Python – reading and writing files

??? ???two ways to open a file open and file ??? How to write to relative and absolute paths?

To Write a file #written to C:\Users\jrw\workspace\Python1 file = open("newfile.txt", "w") file.write("Hello World \n") file.close()

#written to C:\Users\jrw\workspace\Python1 file = open("newfile2.txt", "w") file.write("Hello") file.write("World") file.close() #writes HelloWorld Note: you need to include “\n” for newline.

“””triple quotes””” file = open("newfile3.txt", "w") file.write(""" Hello Again""") file.close() #will write the following Hello Again

What does this write? #written to C:\Users\jrw\workspace\Python1 file = open("newfile4.txt", "w") file.write("Hello") file.close() file = open("newfile4.txt", "w") file.write("Again") file.close()

What does this write? #written to C:\Users\jrw\workspace\Python1 file = open("newfile5.txt", "w") file.write("Hello") file.write("Again") file.close()

Printing to a file file = open("newfile5.txt", "w") print >> file, "START OF FILE" print >> file, "END OF FILE" del file #this will print directly to a file #del file deletes the file object and allows contents to be written to file.

Appending a File with open("test.txt", "a") as myfile: myfile.write("appended text")

Reading a line of a File input1 = file("newfile5.txt", "r") print input1.readline() #this will also read the “\n” at the end of line

Read a file input1 = file("newfile5.txt", "r") print input1.read() #this will read the remainder of a file

Reads a file into a list with open("newfile5.txt") as f: contents = f.readlines() for content in contents: print content ??? Read a file into an array. ??? Number of lines in a file

Iterate through a file (line by line) input1 = file("newfile5.txt", "r") for line in input1.readlines(): print str(len(line)) + " " + line #adds the length of a line to the start of each line

File Exceptions A file or directory (path) does not exist. You do not have read/write permissions Disk error try: fh = open("output/testfile1.txt", "w") fh.write("This is my test file for exception handling!!") except IOError: print "Error: can\'t find file or read data" else: print "Written content in the file successfully" fh.close()

Enter A Number while True: try: x = int(raw_input("Please enter a number: ")) break except ValueError: print "Oops! That was no valid number. Try again" print "you entered" + str(x)

Path - join import os.path filePath = os.path.join("output", "file1.txt") #output\file1.txt fh = open(filePath, "w") fh.write("in file output\file1.txt on Windows machine")

Path - split import os.path filePath = os.path.split("output/file1.txt") (pathName, fileName) = filePath print pathName # output print fileName # file1.txt

Path – split recursively import os.path def split_fully(path): parent_path, name = os.path.split(path) if name == "": return (parent_path, ) else: return split_fully(parent_path) + (name, ) split_fully("dir1/dir2/file1.txt") #('', 'dir1', 'dir2', 'file1.txt')

Splitting file extensions import os.path print os.path.splitext("file.txt") #('file', '.txt')

If a path exists print os.path.exists("C:\Users\jrw\file. txt") #returns true or false