---
title: "Reading data: cheat sheet"
subtitle: "Data detective"
---

# Reading data

> The commands and patterns from this unit. In the tutorial, open **Reference** in any playground to copy them.

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**running total**: Start the total at 0 once, then add to it on every pass.

```python
total = 0
while total < 10:
    total += int(input("Add: "))
```

:::

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**if / else**: Do one thing or the other, depending on a condition.

```python
if x > 0:
    pass
else:
    pass
```

:::

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**variable**: Give a value a name, so you can reuse and change it.

```python
size = 50
```

:::

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**grow value**: Change a value every pass: read the old one, store a new one.

```python
size = 5
for i in range(20):
    forward(size)
    right(90)
    size = size + 5
```

:::

:::keep-together

**for each item**: Work through a list, one item at a time.

```python
for c in colours:
    pass
```

:::

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**print**: Show text or a value in the output box.

```python
print("Hello")
```

:::

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**join text**: Join pieces of text into one with +. Spaces only appear where they are inside the quotes.

```python
"Hello, " + name
```

:::

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**dictionary**: Values stored under names (keys). One dictionary can hold everything about one thing.

```python
star = {"speed": 5, "points": 1}
```

:::

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**dictionary value**: The value stored under that key. The key goes in quotes. Assign to it to change it: star["speed"] = 8.

```python
star["speed"]
```

:::

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**in**: True if the item is in the list (or the key is in the dictionary, or the letters are in the text).

```python
if item in bag:
    pass
```

:::

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**read a file**: Opens the file to read and gives you all of it as one piece of text.

```python
with open("save.txt") as f:
    text = f.read()
```

:::

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**read a CSV**: Each row of the file becomes a dictionary, keyed by the column names in the first line. Every value is text.

```python
import csv

with open("music.csv") as f:
    rows = list(csv.DictReader(f))
```

:::