Title

class: center, middle

# Caesar ciphers

* Letter-by-letter enciphering

---

# The [string module](http://docs.python.org/3.3/library/string.html) is your friend

```python
import string
string.ascii_letters
string.ascii_lowercase
string.ascii_uppercase
string.digits
string.punctuation
```

---

# Doctest

* Why document?
* Why test?

---

# The magic doctest incantation

```python
if __name__ == "__main__":
    import doctest
    doctest.testmod()
```

---

# Doing all the letters

## Abysmal

```python
ciphertext = ''
for i in range(len(plaintext)):
    ciphertext += caesar_encipher_letter(plaintext[i], key)
```

---

# Doing all the letters

## (Merely) Bad

```python
ciphertext = ''
for p in plaintext:
    ciphertext += caesar_encipher_letter(p, key)
```

---

# Doing all the letters

## Good (but unPythonic)

```python
ciphertext = map(lambda p: caesar_encipher_letter(p, key), plaintext)
```

---

# Doing all the letters

## Best

```python
ciphertext = [caesar_encipher_letter(p, key) for p in plaintext]
```