Python學習隨記-字符串（一）

字符串

• 字符串是以單引號或雙引號括起來的任意文本，例 ‘abc’、”def”。
• 字符串是不可變的。

創建字符串：

str1 = "hello world"

字符串運算：

字符串比較大小：

• 從第一個字符開始比較，誰的ASCII值大誰就大，如果相等會比較下個字符的ASCII值的大小。

字符串連接：

str1 = "you are a "
str2 = "good boy"
str3 = str1 + str2
print("str3 =", str3)
# 結果爲：str3 = you are a good boy

輸出重複字符串：

str1 = "good boy "
str2 = str1 * 3
print("str3 =", str2)
# 結果爲：str3 = good boy good boy good boy

訪問字符串中的某一個字符：

• 通過索引下標查詢字符，索引從0開始。

str1 = "you are a good boy "
print(str1[10])
# 結果爲：g

str1[10] = "a"
print("str1 =", str1)
'''
結果爲：
File "Q:/pycharm_project/stringDemo.py", line 4, in <module>
    str1[10] = "a"
TypeError: 'str' object does not support item assignment
證明：字符串是不可變的。
'''

截取字符串：

str1 = "you are a good boy"
# 從給定下標開始截取到給定下標之前
str2 = str1[10:15]
print("str2 =", str2)

# 從頭截取到給定下標之前
str3 = str1[:15]
print("str3 =", str3)

# 從給定下標開始截取到結尾
str4 = str1[15:]
print("str4 =", str4)
str5 = str1[15:25]
print("str5 =", str5)

'''
結果爲：
str2 = good 
str3 = you are a good 
str4 = boy
str5 = boy
'''

判斷字符串包含關係：

str1 = "you are a good boy"
print("good" in str1)
print("good1" in str1)

print("good" not in str1)
print("good1" not in str1)

'''
結果爲：
True
False
False
True
'''

格式化輸出：

str1 = "you are a good boy"
num = 10
f1 = 7.8888888

print("str1 =", str1)
print("num =", num)
print("num =", num, "str1 =", str1)

# %d，%s，%f佔位符
print("num = %d, str1 = %s, f1 = %f" % (num, str1, f1))
print("num = %d, str1 = %s, f1 = %.3f" % (num, str1, f1))

'''
結果爲：
str1 = you are a good boy
num = 10
num = 10 str1 = you are a good boy
num = 10, str1 = you are a good boy, f1 = 7.888889
num = 10, str1 = you are a good boy, f1 = 7.889
'''