Basics of Strings
In Python, strings are sequences of characters enclosed in either single (`'...'`) or double (`"..."`) quotes. This flexibility allows you to easily include quotes within your strings without escaping them:
```python
# Both are valid
single_quote_string = 'Hello, world!'
double_quote_string = "Hello, world!"
```
Special characters, such as newline (`\n`), behave the same in both types of quotes. To include quotes within a string without escaping, you can switch to the other quote type:
```python
quote_in_single = 'He said, "Hello!"'
quote_in_double = "It's a beautiful day."
```
To escape quotes within the same type, use a backslash (`\`):
```python
escaped_single = 'It\'s a beautiful day.'
escaped_double = "He said, \"Hello!\""
```
Raw Strings
Raw strings, prefixed with `r`, treat backslashes as literal characters. This is useful for regular expressions and file paths:
```python
raw_string = r"C:\Users\name\path"
```
Note: A raw string cannot end with an odd number of backslashes due to how escaping works.
Multi-line Strings
Triple quotes (`'''...'''` or `"""..."""`) allow strings to span multiple lines. Line breaks within the triple quotes are included in the string:
```python
multi_line_string = """This is a
multi-line string."""
```
To prevent a line break, end the line with a backslash:
```python
single_line = """This is a \
single-line string."""
```
String Operations
Strings can be concatenated using the `+` operator and repeated using `*`:
```python
concat = "Hello, " + "world!"
repeat = "Ha" * 3
```
Adjacent string literals are automatically concatenated:
```python
auto_concat = "Hello, " "world!"
```
However, this does not work with variables:
```python
var1 = "Hello, "
var2 = "world!"
# This will raise an error
auto_concat_variables = var1 var2
```
Use `+` for concatenating variables:
```python
concat_variables = var1 + var2
```
Indexing and Slicing
Strings can be indexed and sliced. Indexing retrieves individual characters, with the first character at index 0:
```python
s = "Python"
first_char = s[0] # 'P'
```
Negative indices count from the right:
```python
last_char = s[-1] # 'n'
```
Slicing retrieves substrings:
```python
substring = s[1:4] # 'yth'
```
Omitted indices default to the start or end of the string:
```python
slice_from_start = s[:2] # 'Py'
slice_to_end = s[2:] # 'thon'
```
Immutability and Length
Strings are immutable. Any operation that modifies a string creates a new one:
```python
new_s = s.replace("P", "J")
```
The `len()` function returns the length of a string:
```python
length = len(s) # 6
```
String Methods and f-strings
Strings come with numerous methods for transformation and searching. Additionally, f-strings (`f"..."`) allow embedded expressions:
```python
name = "Alice"
greeting = f"Hello, {name}!"
```
