# 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")
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.arkannis.net/programming/courses/python-pcap-31-03-course/file-io-and-exception-handling/file-io.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.