Input_Output_en_US.md

Input & Output

This chapter will discuss some basic I/O functions.

[Code sample]

Output To Screen

Using print() to print strings to screen.

>>> print("Print")
Print

Using .format(*args) with {} in the string to format the output:

>>> print("{0} and {1}.\n1: {1}, 0: {0}".format("First", "Second"))
First and Second.
1: Second, 0: First

Get Input String

Using input(prompt="") to get the input (string).

>>> x = input("enter a number for x? ")
enter a number for x? 10
>>> print(type(x))
<class 'str'>
>>> print(x)
10

File Handling

Using open(filename, mode="rt") to work with files.

! Always don't forget to close .close() the opened file.

There has some different modes:

Mode	Description
r	Read (default). Only for file reading, error if file does not exist.
a	Append. Append text to the file, create file if file does not exist.
w	Write. Overwrite the file, create file if file does not exist.
x	Create. Create the file, error if file exists

Also, you can specify the file type. Add it after the mode:

Type	Description
t	Text (default)
b	Binary

Add + for read and write the file:

file = open(filename, mode="r+")    # from the beginning
file = open(filename, mode="w+")    # from the beginning, overwrite.
file = open(filename, mode="a+")    # from the end

file.close()

Read File

Using read(length) to read file.

hello_world.txt:

Hello, 
Python!

read file:

>>> file = open("hello_world.txt", "r")
>>> print(file.read())
Hello, 
Python!
>>> print(file.read(3))
Hel
>>> file.close()

Also, in another way:

file_content = ""
file = open("hello_world.txt", "r")

for line in file:
    file_content += line

print(file_content)
# Hello,
# Python!

file.close()

Write File

Using write() to write string to file.

According to the mode, it will append or overwrite.

file = open("hello_world.txt", "w")
file.write("Hello, world!")        # overwrite
file.close()

file = open("hello_world.txt", "r")
print(file.read())
# Hello, world!