# 文字字串
### Story about string
---
<!-- .slide: data-background="https://hackmd.io/_uploads/ByB5Vi_bC.jpg" -->
## About Me
- Yoyo
- Volunteer of PyCon TW since 2022
- 雙棲 Backend + AI 工程師
---
## 字串
```python
ss = "這是一個字串"
aa = '這也是一個字串'
print(ss) # 這是一個字串
print("這串字總共有" + str(len(ss)) + "個字") # 字串加法
five = 5
print(str(five) * five) # 字串乘法，輸出：55555
# 多行字
s_long = """
這串字有好多行
This string contains multiple lines.
"""
print(s_long)
```
----
## 特殊字元
```python
newline = "\n"
tab = "\t"
raw_str = r"這裡面\n不會被換行"
extra_quote = "這裡面多了一個\"雙引號"
```
---
## String <=> Byte 轉換
```python
s1 = "I am byte man"
s2 = b"I am byte man"
print(type(s1), type(s2)) # str, bytes
print(s1 == s2) # False
print(s1.encode("UTF8") == s2) # True
print(s1 == s2.decode("UTF8")) # True
```
---
## 基本操作
----
### `split`
```python
ss = "你我，相隔兩地 卻又彼此糾纏"
# 依照空格分開
print(ss.split()) # 你我，相隔兩地 / 卻又彼此糾纏
# 依照指定字元分開
print(ss.split("，")) # 你我 / 相隔兩地 卻又彼此糾纏
```
### `strip`
<font size=5>
移除前方與後方的空格、特殊字元
</font>
```python
ss = " 清空前方與後方障礙 中間不受影響 \n"
print(ss.strip()) # "清空前方與後方障礙 中間不受影響"
```
----
### `replace`, `index`
```python
ss = "Hello, I am Yoyo"
print(ss.replace("Yoyo", "Gobby")) # Hello, I am Gobby
print(ss.index("Yoyo")) # 12
```
----
### `startswith`, `endswith`
```python
ss = "Today is so HOT"
print(ss.startswith("Tod")) # True
print(ss.endswith("OT")) # True
```
----
### 變換大小寫
```python
ss = "Hello there. Nice to meet you~"
print(ss.lower()) # hello there. nice to meet you~
print(ss.upper()) # HELLO THERE. NICE TO MEET YOU~
print(ss.title()) # Hello There. Nice To Meet You~
print(ss.swapcase()) # hELLO THERE. nICE TO MEET YOU~
```
----
### `join`
```python
ss = "啊啊啊，是逗號"
s_list = ss.split("，")
print("-".join(s_list)) # 啊啊啊-是逗號
```
----
### in 判斷
```python
ss = "People mountain people sea"
print("peop" in ss) # True
print(" sea" in ss) # True
```
----
### Indexing & slicing
<font size=5>
後面的單元會更詳細介紹 slicing，這邊先提供參考
</font>
```python
ss = "Hello, Foo Bar"
print(ss[0]) # "H"
print(ss[-1]) # "r"
print(ss[1:3]) # "el"
print(ss[:3]) # "Hel"
print(ss[-3:]) # "Bar"
print(ss[4::-1]) # "olleH"
```
---
## 格式化你的字串
<font size=6>
方便將不同變數儲存的內容，組合成一個完整的句子
</font>
```python
name = "Yoyo"
print(f"你好，{name}") # 你好，Yoyo
# 實務上的應用之一
formatter = logging.Formatter("%(asctime)s [%(levelname)s] %(message)s [at %(filename)s:%(lineno)d]")
handler = logging.StreamHandler()
handler.setFormatter(formatter)
logger = logging.getLogger()
logger.addHandler(handler)
logger.setLevel(logging.INFO)
logger.info("Hello Python") # 2024-04-30 20:03:00 [INFO] Hello Python [at main.py:10]
```
---
## 幾種不同格式化的方法
#### % - 過時的方法
`print("你好，%s" % name)`
#### .format - 還行
`print("你好，{}".format(name))`
#### f-string - 最新流行
`print(f"你好，{name}")`
---
## .format
```python
name = "Yoyo"
year = 18
print("我是{}，今年{}歲".format(name, year)) # 我是Yoyo，今年18歲
print("我是{1}，今年{0}歲".format(year, name))
print("我是{name}，今年{year}歲".format(name=name, year=year))
# 格式化小數點
height = 159.66666666
print("我身高{:.1f}公分".format(height)) # 我身高159.7公分
```
---
## Padding
----
強迫症發作...
----
排序亂掉
---
## Padding - 向右看～～起！！
```python
print(f"新兵 {1:02} 號，身上有 {1:7} 塊美金！")
print(f"新兵 {2:02} 號，身上有 {203:7} 塊美金！")
print(f"新兵 {13:02} 號，身上有 {9885.2:7,} 塊美金！")
```
酥胡～～
----
整齊了～～
----
#### 向左向中看～～齊！
```python
print(f"The {'world':<10} is beautiful")
print(f"The {'world':^10} is beautiful")
print(f"The {'world':@^10} is beautiful")
```
---
### f-string 黑魔法
```python
a = "Yeah"
b = 123
c = 1.234567
print(f"{a=} / {b=} / {c=:10.5f}") # a='Yeah' / b=123 / c= 1.23457
```
---
<!-- .slide: data-background="https://hackmd.io/_uploads/Sk6dWsdb0.jpg" -->
# 感謝大家的收聽～
學海無涯，學習 Python 的前方依舊是漫漫長路
---
## References
- [Colab](https://colab.research.google.com/drive/1nQmPA6uaguR3tUpd5zmNpoND82sFGPbv?usp=sharing)
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