Python exercise - determining whether a string is a decimal

# Homework 1： Determine whether a string is a decimal 
def is_float(string):
string1 = str(string)
if string1.count('.') > 1: # Detect the number of decimal points in the string 
return ' The string is not a decimal '
elif string1.isdigit(): # Checks whether a string is made up of numbers only , Returns if the string contains only numbers True Otherwise return to False
return ' The string is not a decimal '
else:
new_string = string1.split(".") # Divide characters by decimal point 
first_num = new_string[0] # Take this after segmentation list The first element of 
# Judge the number of minus signs and first_num The first element is not "-", If the number of minus signs equals 1 also firs_num The first element is "-", Then it's legal 
if first_num.count( '-') == 1 and first_num[0] == '-':
first_num = first_num.replace('-','')
if first_num.isdigit() and new_string[1].isdigit():
return ' The string is decimal '
else:
return ' The string is not a decimal '
if __name__ == '__main__':
while True:
print(" Input Q Exit procedure ")
string = input(" Determine whether a string is a decimal , Please enter a string ：")
if string.upper() == 'Q':
print(" You quit the program ")
break
print(is_float(string))
print('\n')

Knowledge points involved :

notes ： The following references are from Novice tutorial

• count()
  describe
  Python count() Method is used to count the number of characters in a string . The optional parameters are at the beginning and end of the string search .
  grammar
  count() Method syntax ：str.count(sub,start=0,end=len(string))
  Parameters
  sub - - Search for substrings .
  start - - Where the string starts searching . The default is the first character , The first character index value is 0.
  end - - Where to end the search in the string . The index of the first character in the character is 0. Default to the last position of the string .
  Return value
  This method returns the number of times the substring appears in the string .
  example

str = "this is string happy!!!";
sub = "i";
print("str.count(sub, 4, 30) : ", str.count(sub, 4, 30))
sub = "is";
print("str.count(sub) : ", str.count(sub))
# give the result as follows 
# str.count(sub, 4, 30) : 2
# str.count(sub) : 2

• isdigit()
  describe
  Python isdigit() Method to detect whether the string consists of only numbers
  grammar
  isdigit() Method syntax ：str.isdigit()
  Parameters
  nothing
  Return value
  Returns if the string contains only numbers True No one returns False
  example

str = "123456" # Only this string of numbers 
print(str.isdigit())
# result ：True
str1 = "this is string!!!"
print(str1.isdigit())
# result ：False

• split()
  describe
  Python split() Slice a string by specifying a separator , If parameters num There is a specified value , Then separate num+1 Substring
  grammar
  split() Method syntax ：str.split(str="",num=string.count(str))
  Parameters
  str - - Separator , The default is all empty strings , Including Spaces 、 Line break (
  n)、 tabs (\t) etc. .
  num - - Number of divisions . The default is -1, To separate all .
  Return value
  Returns a list of split strings
  example

str = "Line1-abcdef \nLine2-abc \nLine4-abcd";
print(str.split( )) # Space as separator , contain \n
print(str.split(' ', 1 )) # Space as separator , Separate into two 
# Output results 
# ['Line1-abcdef', 'Line2-abc', 'Line4-abcd']
# ['Line1-abcdef', '\nLine2-abc \nLine4-abcd']
txt = "Google#Runoob#Taobao#Facebook"
x = txt.split("#", 1) # The second parameter is 1, Returns a list of two parameters 
print(x)
# Output results : ['Google', 'Runoob#Taobao#Facebook']

• upper()
  describe
  Python upper() Method to convert lowercase letters in a string to uppercase letters .
  grammar
  upper() Method syntax ：str.upper()
  Parameters
  NA
  Return value
  Returns a string that converts lowercase letters to uppercase letters .
  example

str1 = "this is string!!!"
print("str.upper():",str.upper())
# Output results : str.upper(): THIS IS STRING HAPPY!!!

• break
  Python in break and continue Explain in detail the usage and differences of

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