# In learning Python, we must read this knowledge again. It doesn't matter if we can't remember it. We must know the common function usage of strings

### str.index(sub, start=None, end=None)

Function: check whether the sub is in the string. If yes, the index will be returned, and only the index matched for the first time will be returned; If it cannot be found, an error will be reported; You can specify the statistical range, [start,end) left closed interval and right open interval

```str = "helloworldhhh"
print(str.index("h"))
print(str.index("hhh"))
```

results of enforcement

```0
10
```

### str.find(sub, start=None, end=None)

Function: the same as index(), but no error will be reported if it is not found, but - 1 will be returned

```str = "helloworldhhh"
print(str.find("h"))
print(str.find("hhh"))
print(str.find("test"))
```

results of enforcement

```0
10
-1
```

### str.count( sub, start=None, end=None)

Function: count the number of substrings; you can specify the statistical range, [start,end) left closed interval and right open interval

```'''
No one answers the problems encountered in learning? Xiaobian created one Python exchange of learning QQ Group: 725638078
Look for like-minded friends to help each other,There are also good videos and tutorials in the group PDF e-book!
'''
str = "hello world !!! hhh"

print(str.count(" "))
print(str.count(" ", 5, 10))
```

results of enforcement

```3
1
```

### str.split(str="", num=string.count(str))

Function: divide strings into lists according to str. if the parameter num has a specified value, separate num+1 substrings

```str = "hello world !!! hhh"

print(str.split(" "))
print(str.split(" ", 1))
```

results of enforcement

```['hello', 'world', '!!!', 'hhh']
['hello', 'world !!! hhh']
```

### str.strip(chars = " ")

Function: removes the character sequence chars specified at the beginning and end of the string. The default is space

### str.lstrip(chars = " ")

Function: removes the character sequence chars specified in the string header. The default is space

### str.rstrip(chars = " ")

Function: removes the character sequence chars specified at the end of the string. The default is space

```str = "   hello  every  "

print("1", str.strip(), "1")
print(str.lstrip(), "1")
print("1", str.rstrip())

str = "!!! cool !!!"

print(str.strip("!"))
```

results of enforcement

```1 hello  every 1
hello  every   1
1    hello  every
cool
```

### str.replace(old,new,count= -1)

Function: replace old (old string) with new (new string) in the string. count represents the maximum number of replacement times. The default - 1 represents all replacement

```'''
No one answers the problems encountered in learning? Xiaobian created one Python exchange of learning QQ Group: 725638078
Look for like-minded friends to help each other,There are also good videos and tutorials in the group PDF e-book!
'''
str = "hello world !!! hhh"

print(str.replace(" ", "-"))
print(str.replace(" ", "-", 1))
```

results of enforcement

```hello-world-!!!-hhh
hello-world !!! hhh
```

### str.join(sequence)

Function: connect the elements in the sequence with the specified characters to generate a new string

```lists = ["1", "2", "3"]
tuples = ("1", "2", "3")

print("".join(lists))
print("".join(tuples))
print("-".join(lists))
```

results of enforcement

```123123
1-2-3
```

### str.upper()

Function: change all strings into uppercase letters

### str.lower()

Function: change all strings into lowercase letters

### str = "hello world !!! hhh"

```print(str.upper())
print(str.lower())
```

results of enforcement

```HELLO WORLD !!! HHH
hello world !!! hhh
```

### str.startswith(prefix, start=None, end=None)

Function: check whether the string starts with the specified substring. If so, return True; otherwise, return False; you can specify the statistical range, [start,end) left closed interval and right open interval

### str.endswith(self, suffix, start=None, end=None)

Function: on the contrary, this is the end

```'''
No one answers the problems encountered in learning? Xiaobian created one Python exchange of learning QQ Group: 725638078
Look for like-minded friends to help each other,There are also good videos and tutorials in the group PDF e-book!
'''
str = "hello world !!! hhh"

print(str.startswith("h"))
print(str.startswith("hh"))
print(str.endswith("h"))
print(str.endswith("hhhh"))
```

results of enforcement

```True
False
True
False
```

### str.isdigit()

Function: check whether the string is only composed of numbers

```str = "123134123"

print(str.isdigit())
```

results of enforcement

```true
```

str.isalpha()

Function: check whether the string is only composed of letters

str = "abc"

print(str.isalpha())

results of enforcement

true

### str.splitlines([keepends])

Function: separate strings by lines ('\ r', '\ r\n', \ n ')

```str = """
123
456
789
"""

print(str.splitlines())

with open("./file1.txt", encoding="utf-8") as f:
print(lists)
```

results of enforcement

```['', '123', '456', '789']
['name: Jack   ;    salary:  12000', ' name :Mike ; salary:  12300', 'name: Luk ;   salary:  10030', '  name :Tim ;  salary:   9000', 'name: John ;    salary:  12000', 'name: Lisa ;    salary:   11000']
```

At the end, I recommend a very good learning tutorial for you. I hope it will be helpful for you to learn Python!

Python basics tutorial recommendation

Python crawler case tutorial recommendation

Tags: Python Back-end

Posted on Sat, 06 Nov 2021 02:21:43 -0400 by _tina_