# File IO

## How to open a file

```python
# Syntax:
my_file = open('<location_to_file>/<file_name>')
```

## To read that file:

```python
content = myfile.read()

# To print the content
print(content)
```

#### Particular read case

```python
content = myfile.read()

data = myfile.read()

print(content)
print(data)
```

* The `content` variable will be printed to screen and does work
* But the `data` variable will not print anything to screen

#### Why does this happen?

* It has to do of how the `.read()` method works:
  * It takes the cursor and moves it all the way to the end of the file
  * It does not go back
  * So when printing the second read, the cursor is already at the end of the file

## To reset the cursor:

```python
content = myfile.read()
print(content)

myfile.seek(0) # Resets the cursor back to position 0

data = myfile.read()
print(data)
```

* Method `myfile.seek(0)` sets the cursor back to char 0 i.e the beginning of the file

## Add each line of file to a list:

```python
# Saves each line as a separate element in a list
content_list = myfile.readlines()

print(content_list)
```

## Closing the file:

* If you are reading the file using the above methods, you also want to make sure you are closing the file
* You cannot have 2 threads doing things with the same file with the above methods

```python
# Closing the file
myfile.close()
```

## Another way of opening a file is with the `with` clause:

* By using the `with` syntax, you automatically `open` and `close` the file

```python
# Syntax:
with open(<file_location>/<file_name>) as <variable_name_you_want_to_use>:
	content = variable_name_you_want_to_use.read()

print(content)
```

* This `open` function also has another argument that it can take, which is the `mode=`
  * a = append - writes at the end
  * w = write - overwrite the file
  * r = read - only reads from file, cannot write to it (error: `not writable`)
  * r+ = read and write to the file
  * w+ = used for overwriting a file and reading it after

```python
with open(file_name, mode='a') as myfile:
	# Will be appended at the end of the file
	myfile.write("\nWrite a sentence") # Will also append on new line
```

* If you change the filename or it does not exist it will create a new file automatically

```python
with open(new_file_name, mode='a') as myfile:
	myfile.write("\nWrite a sentence")
```

* By using `r+` it will overwrite the characters starting from the beginning of the file

```python
with open(new_file_name, mode='r+') as myfile:
	myfile.write("\nWrite a sentence")
```