String
Like many other popular programming languages, strings in Python are arrays of bytes representing unicode characters.
However, Python does not have a character data type, a single character is simply a string with a length of 1.
Square brackets can be used to access elements of the string
a = "Hello, World!"
print(a[1]) # e
'hello' is the same as "hello".
multiline string
a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."""
print(a)
looping through a string
for x in 'wangenius':
print(x)
len()
x = "wangenius"
print(len(x)) # 9
check string
txt = "The best things in life are free!"
print("free" in txt) # true
if "free" in txt:
print("Yes, 'free' is present.")
print("expensive" not in txt) # true
切片
左闭右开
b = "Hello, World!"
print(b[2:5])
print(b[:5]) # slice frome the beginning of the string
print(b[2:]) # slice to the end of the string
The first character has index 0.
Use negative indexes to start the slice from the end of the string:
b = "Hello, World!"
print(b[-5:-2]) # orl -5，-4，-3.
修改
a = "Hello, World!"
print(a.upper())
print(a.lower())
# removes any whitespace from the beginning or the end:
print(a.strip()) # returns "Hello, World!"
# replaces a string with another string
print(a.replace("H", "J"))
# The split() method returns a list where the text between the specified separator becomes the list items.
print(a.split(",")) # returns ['Hello', ' World!']
Concatenation
a = "Hello"
b = "World"
c = a + b
d = a + " " + b;
print(c) # HelloWorld
print(d) # Hello World
格式化
age = 36
txt = "My name is John, I am " + age # ❎we cannot combine strings and numbers like this
print(txt)
quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))
But we can combine strings and numbers by using the format() method!
成员方法
| Method | Description |
|---|---|
| capitalize() | Converts the first character to upper case |
| casefold() | Converts string into lower case |
| center() | Returns a centered string |
| count() | Returns the number of times a specified value occurs in a string |
| encode() | Returns an encoded version of the string |
| endswith() | Returns true if the string ends with the specified value |
| expandtabs() | Sets the tab size of the string |
| find() | Searches the string for a specified value and returns the position of where it was found |
| format() | Formats specified values in a string |
| format_map() | Formats specified values in a string |
| index() | Searches the string for a specified value and returns the position of where it was found |
| isalnum() | Returns True if all characters in the string are alphanumeric |
| isalpha() | Returns True if all characters in the string are in the alphabet |
| isascii() | Returns True if all characters in the string are ascii characters |
| isdecimal() | Returns True if all characters in the string are decimals |
| isdigit() | Returns True if all characters in the string are digits |
| isidentifier() | Returns True if the string is an identifier |
| islower() | Returns True if all characters in the string are lower case |
| isnumeric() | Returns True if all characters in the string are numeric |
| isprintable() | Returns True if all characters in the string are printable |
| isspace() | Returns True if all characters in the string are whitespaces |
| istitle() | Returns True if the string follows the rules of a title |
| isupper() | Returns True if all characters in the string are upper case |
| join() | Joins the elements of an iterable to the end of the string |
| ljust() | Returns a left justified version of the string |
| lower() | Converts a string into lower case |
| lstrip() | Returns a left trim version of the string |
| maketrans() | Returns a translation table to be used in translations |
| partition() | Returns a tuple where the string is parted into three parts |
| replace() | Returns a string where a specified value is replaced with a specified value |
| rfind() | Searches the string for a specified value and returns the last position of where it was found |
| rindex() | Searches the string for a specified value and returns the last position of where it was found |
| rjust() | Returns a right justified version of the string |
| rpartition() | Returns a tuple where the string is parted into three parts |
| rsplit() | Splits the string at the specified separator, and returns a list |
| rstrip() | Returns a right trim version of the string |
| split() | Splits the string at the specified separator, and returns a list |
| splitlines() | Splits the string at line breaks and returns a list |
| startswith() | Returns true if the string starts with the specified value |
| strip() | Returns a trimmed version of the string |
| swapcase() | Swaps cases, lower case becomes upper case and vice versa |
| title() | Converts the first character of each word to upper case |
| translate() | Returns a translated string |
| upper() | Converts a string into upper case |
| zfill() | Fills the string with a specified number of 0 values at the beginning |