> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/python/cpython/llms.txt
> Use this file to discover all available pages before exploring further.

# csv - CSV File Reading and Writing

> CSV file reading and writing

The `csv` module implements classes to read and write tabular data in CSV format.

## Module Import

```python theme={null}
import csv
```

## Reading CSV Files

### csv.reader()

```python theme={null}
import csv

with open('data.csv', 'r') as f:
    reader = csv.reader(f)
    for row in reader:
        print(row)  # List of values
```

### DictReader

```python theme={null}
import csv

with open('data.csv', 'r') as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row)  # OrderedDict with column names as keys
        print(row['name'], row['age'])
```

## Writing CSV Files

### csv.writer()

```python theme={null}
import csv

data = [
    ['Name', 'Age', 'City'],
    ['Alice', 30, 'NYC'],
    ['Bob', 25, 'LA'],
]

with open('output.csv', 'w', newline='') as f:
    writer = csv.writer(f)
    writer.writerows(data)
```

### DictWriter

```python theme={null}
import csv

data = [
    {'name': 'Alice', 'age': 30, 'city': 'NYC'},
    {'name': 'Bob', 'age': 25, 'city': 'LA'},
]

with open('output.csv', 'w', newline='') as f:
    fieldnames = ['name', 'age', 'city']
    writer = csv.DictWriter(f, fieldnames=fieldnames)
    
    writer.writeheader()
    writer.writerows(data)
```

## Dialects and Formatting

```python theme={null}
import csv

# Custom delimiter
with open('data.tsv', 'r') as f:
    reader = csv.reader(f, delimiter='\t')
    for row in reader:
        print(row)

# Quote all fields
with open('output.csv', 'w', newline='') as f:
    writer = csv.writer(f, quoting=csv.QUOTE_ALL)
    writer.writerow(['Name', 'Description'])
    writer.writerow(['Product', 'This is a "quoted" field'])
```

## Practical Example

```python theme={null}
import csv

# Process CSV data
with open('sales.csv', 'r') as f:
    reader = csv.DictReader(f)
    total = sum(float(row['amount']) for row in reader)
print(f"Total sales: ${total}")

# Export data to CSV
data = [
    {'product': 'Widget', 'price': 10.50, 'quantity': 5},
    {'product': 'Gadget', 'price': 25.00, 'quantity': 3},
]

with open('export.csv', 'w', newline='') as f:
    writer = csv.DictWriter(f, fieldnames=['product', 'price', 'quantity'])
    writer.writeheader()
    writer.writerows(data)
```

<CardGroup cols={2}>
  <Card title="json" href="/library/json">
    JSON encoding/decoding
  </Card>

  <Card title="io" href="/library/io">
    Core I/O operations
  </Card>
</CardGroup>