Python学习笔记（2）-- if/for/while/字符串操作

 

•  if语句
  
•  for语句
•  while语句
•  字符串运算符
•  字符串逆序
•  字符串大小写
•  字符串查找
•  字符串编码
•  字符串判断
•  字符串join/split/count

---

 

if语句

"""
if 表达式：
    表达式成立
else:
    不成立
"""
a = 10
b = 20
if a > b:
    print(a)
else:
    print(b)

---

for语句

for i in range(0, 10):
    print(i)
else:
    print("finish")

else：后面语句为结束循环执行，continue导致的结束也会执行

pass：过渡语句（do nothing）

continue：跳过本次循环

break：跳出循环（不会执行else语句）

---

 

while语句

i = 0
while i < 4:
    i += 1
    print(i)
else:
    print("finish")

---

字符串运算符

a = "Peter"
b = "Peter"
print(a == b)           # True
print(a is b)           # True
print(a + b)            # PeterPeter
print(a * 5)            # PeterPeterPeterPeterPeter
print("e" in a)         # True
print("e" not in a)     # False

---

字符串逆序

a = "Peter"
b = "Peter"
print(a[1])             # e
print(a[0:3:1])         # Pet
print(a[-1:-4:-1])      # ret [开始：结束：间隔（负数倒序）]
print(a[::-1])          # reteP 字符串倒序

---

字符串大小写

message = "i am a good man"
print(message.capitalize())     # I am a good man
print(message.title())          # I Am A Good Man
print(message.upper())          # I AM A GOOD MAN
print(message.lower())          # i am a good man

---

字符串查找

word = "hello world"
print(word.find("l", 0, len(word)))
print(word.find("w", 0, len(word)))
print(word.rfind("l"))
print(word.index("l"))  # 找不到不返回异常
print(word.replace("world", "me"))

---

字符串编码

word = "hello world"
print(word.encode("utf-8"))
word = word.encode("utf-8")
print(word.decode("utf -8"))

---

字符串判断

file = "boy.jpg"
print(file.startswith("boy"))
print(file.endswith("jpg"))

---

字符串join/split/count

join用字符串拼接，拼接为字符串则拆开字母，拼接为列表则元素拆开

a = "boy"
print("-".join(a))  # b-o-y

split返回列表

b = "b-o-y"
print(b.split("-"))

count统计字符串中的字母

word = "hello world"
print(word.count("l"))    # 3