## Challenges

Reddit challenges in python language.

Files Code and Result

### challenge3_easy

```''' Welcome to cipher day!

write a program that can encrypt texts with an alphabetical caesar cipher.
This cipher can ignore numbers, symbols, and whitespace.

Plain:    ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher:   XYZABCDEFGHIJKLMNOPQRSTUVW

The encryption can also be represented using modular arithmetic
by first transforming the letters into numbers, according to the scheme,
A = 0, B = 1,..., Z = 25. Encryption of a letter x by a shift n
can be described mathematically as,

E_n(x) = (x + n) \mod {26}.

Decryption is performed similarly,

D_n(x) = (x - n) \mod {26}.

'''

''''
Decrypt
ABCDEFG...... to
XYZABCD......
'''

def encode(letter):
''' str -> str '''
alph = 'abcdefghijklmnopqrstuvwxyz'
indx = alph.index(letter)
shift = (indx - 3) % 26
result = alph[shift]
return result

if __name__ == '__main__':

out = ''
#message = 'retreat we are beat'
message ='retreat'
for letter in message:
if letter.isalpha():
out += encode(letter)
else:
out += ' '
print('Message is {0} and when encrypted it is {1}'.format(message, out))
```

### Result

```Message is retreat and when encrypted it is obqobxq
```