---
title: Python - String, Bytes and ByteArray
tags: python, string
---

[TOC]

---
# String
> Cause string is immutable object, any function changing the string always return a new string object.

## 1. Test Function
- `isalnum()`
- Return True, if string only contains number or alphabet
- `isalpha()`
- Return True, if string only contains alphabet
- `isdigit()`
- Return True, if string only contains number
- 只認阿拉伯數字
- `isnumeric()`
- Return True, if string only contains number
- 不只阿拉伯數字，甚至認得中文

a = '一二三'
a.isnumeric() # True
a.isdigit()   # False

- `isspace()`
- Return True, if string only contains whitespace charactor
- `isidentifier()`
- Return True, if string is python identifier
- `islower()`
- Return True, if string is lower case
- `isupper()`
- Return True, if string is upper case
- `startswith(s)`
- Return True, if string starts with `'s'`
- `endswith(s)`
- Return True, if string ends with `'s'`

## 2. Search Function
- `find(s)`
- Return the first found index of `'s'` in the string which starts from index 0
- Return -1 if `'s'` is not in stirng
- `rfind(s)`
- Return the first found index of `'s'` in the string which starts from last index
- Return -1 if `'s'` is not in stirng
- `count(s)`
- Return how many times `'s'` appers in the string

## 3. Common Function
- `lower()`
- Return string is lower case
- `upper()`
- Return string is upper case
- `strip(char)`
- `rstrip(char)`
- `lstrip(char)`
- `replace(old, new)`
- Return string has replaced old sub_string to new sub_string
- EX:`str.replace('\n', '').replace('\r', '').replace('\t', '')`
- `split(sep=None, maxsplit=-1)`
- Return a list of the words in the string, using sep as the delimiter string.
- EX:`'He ll o'.split(' ') --> ['He', 'll', 'o']`
- `join(iterable)`
- Return a new string that inserted string between the each element in the iterable
- EX:`','.join(['He', 'll', 'o']) --> 'He,ll,o'`

## 4. Format Function
- format sign
- `{:d}`: int
- `{:X.Yf}`: float
- X is total numbers
- Y is the numbers after .
- `{:e} {:E}`: scientific sign
- `{:x} {:X}`: 0x16
- `{:x} {:X}`: 08
- `{:b}`: binary
- simple function
- `{!a}`: ascii()
- `{!s}`: str()
- `{!r}`: repr()
- align
- `{>}`: right
- `{<}`: left
- `{^}`: middle
- general
- `{[arg_name] : [padding] [align] [width]}`
- EX: `'{:_>5}'.format('***')` -> `__***`
- EX: `'{03d}'.format(51)` -> `051`
### format

n = ['one', 'two', 'three']

# By order
'{} {} {}'.format(n[0], n[1], n[2])
# one two three
# By number
'{2} {1} {0}'.format(n[0], n[1], n[2])
# three two one
# By name
'{a} {b} {c}'.format(c=n[0], b=n[1], a=n[2])
# three two one

### f"..."

n = ['one', 'two', 'three']
f'{n[0]} {n[1]} {n[2]}'

### Efficiency
[參考](https://towardsdatascience.com/do-not-use-to-join-strings-in-python-f89908307273)

# Fast
f'{s} {t}'
' '.join((s, t))
'%s %s' % (s, t)
'{} {}'.format(s, t)
Template('$s $t').substitute(s=s, t=t)
# Slow

## 5. Other Functions
- `maketrans(x[, y[, z]])`
- This static method returns a translation table usable for `str.translate()`.
- `x`
- If only one argument is supplied, it must be a **dictionary**.
- The dictionary should contain a **1-to-1 mapping** from **a single character string to its translation OR a Unicode number** (97 for 'a') to its translation.
- `y`
- If two arguments are passed, it must be **two strings with equal length**.
- Each character in the first string is a replacement to its corresponding index in the second string.
- 第一個字串的所有字元會配第二個字串對應位置的字元替換
- `z`
- If three arguments are passed, each character in the third argument is **mapped to None**.
- `translate(table)`
- `table`
- Create by `str.maketrans()`

sample = 'abc def xyz'

table = str.maketrans( {'a': 'z', 'b': 'y', 'c': 'x'} )
sample.translate(table)
# Output: 'zyx def xyz'

table2 = str.maketrans('def', 'zoo')
sample.translate(table2)
# Output: 'abc zoo xyz'

table3 = str.maketrans('', '', 'bey')
sample.translate(table3)
# Output: 'ac df xz'

table4 = str.maketrans('abcdefxyz', '123456789', 'bey')
sample.translate(table4)
# Output: '13 46 79'

---

# String Module
> import string

## Attribute
- `punctuation`

'!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'

---
# Bytes
- It is immutable

## Functions
- `fromhex(hex_string)`
- hex string to bytes

b = bytes.fromhex("0f1c")

- `hex()`
- bytes to hex string

# Create bytes
b = b'\x41\x42'

b = bytes( n for n in range(ord('A'), ord('Z')+1) )

b = 'AB'.encode() # default is UTF-8
b = 'AB'.encode('ascii')

# ByteArray
- It is mutable