Reading Files in Python

  • Download Data in python as shown below. Using wget command. The file is located on a webserver and has name example1.txt 


    • 
# Download Example file

!wget -O /resources/data/Example1.txt https://s3-api.us-geo.objectstorage.softlayer.net/cf-courses-data/CognitiveClass/PY0101EN/labs/example1.txt

  • Reading Text Files One way to read or write a file in Python is to use the built-in open function.


  • The open function provides a File object that contains the methods and attributes you need in order to read, save, and manipulate the file.


  • In this section, we will only cover .txt files. The first parameter you need is the file path and the file name. An example is shown as follow:


  • Reading Text Files


  • The mode argument is optional and the default value is r. In this section we only cover two modes:


    1. r Read mode for reading files


    2. w Write mode for writing files


  • For the next example, we will use the text file Example1.txt. The file is shown as follow:


  • Reading Text Files


  • We read the file: 


    • 
# Read the Example1.txt

example1 = "drive/app/Example1.txt"
file1 = open(example1, "r")

  • We can view the attributes of the file. The name of the file: 


    • 
# Print the path of file

file1.name

  • The mode the file object is in: 


    • 
# Print the mode of file, either 'r' or 'w'

file1.mode

  • We can read the file and assign it to a variable : 


    • 
# Read the file

FileContent = file1.read()
FileContent

  • We can print the file: 


    • 
# Print the file with '\n' as a new line

print(FileContent)

  • The file is of type string: 


    • 
# Type of file content

type(FileContent)

  • We must close the file object: 


    • 
# Close file after finish

file1.close()

  • A Better Way to Open a File Using the with statement is better practice, it automatically closes the file even if the code encounters an exception.


  • The code will run everything in the indent block then close the file object. 


    • 


# Open file using with

with open(example1, "r") as file1:
    FileContent = file1.read()
    print(FileContent)

  • The file object is closed, you can verify it by running the following cell: 


    • 
# Verify if the file is closed

file1.closed

  • We can see the info in the file: 


    • 
# See the content of file

print(FileContent)

  • The syntax is a little confusing as the file object is after the as statement.


  • We also don’t explicitly close the file.


  • Therefore we summarize the steps in a figure:


  • Reading Text Files


  • We don’t have to read the entire file, for example, we can read the first 4 characters by entering three as a parameter to the method .read(): 


    • 
# Read first four characters

with open(example1, "r") as file1:
    print(file1.read(4))

  • Once the method .read(4) is called the first 4 characters are called. If we call the method again, the next 4 characters are called.


  • The output for the following cell will demonstrate the process for different inputs to the method read(): 


    • 


# Read certain amount of characters

with open(example1, "r") as file1:
    print(file1.read(4))
    print(file1.read(4))
    print(file1.read(7))
    print(file1.read(15))

  • The process is illustrated in the below figure, and each color represents the part of the file read after the method read() is called:


  • Reading Text Files


  • Here is an example using the same file, but instead we read 16, 5, and then 9 characters at a time: 


    • 

# Read certain amount of characters

with open(example1, "r") as file1:
    print(file1.read(16))
    print(file1.read(5))
    print(file1.read(9))

  • We can also read one line of the file at a time using the method readline(): 


    • 


# Read one line

with open(example1, "r") as file1:
    print("first line: " + file1.readline())

  • We can use a loop to iterate through each line: 


    • 


# Iterate through the lines

with open(example1,"r") as file1:
        i = 0;
        for line in file1:
            print("Iteration", str(i), ": ", line)
            i = i + 1;

  • We can use the method readlines() to save the text file to a list: 


    • 

# Read all lines and save as a list

with open(example1, "r") as file1:
    FileasList = file1.readlines()

  • Each element of the list corresponds to a line of text: 


    • 

# Print the first line

FileasList[0]

# Print the second line

FileasList[1]

# Print the third line

FileasList[2]