The path to learning in Python day2

The path to learning in Python day2

One: formatted output of the string

Name = "abc" Name2 = 123name3 = 22name4 = "abc\n\t123" ABC = "   name:%s  name2:%d  name3:%f  name4:%r< c6/>name5:%s '% (name,name2,name3,name4,name4) Print (abc)

The result is:

　　　　　　

As the above example, summarize the following bits

%s: Input string

%d: can only output the number, otherwise it will error

%f: Show floating-point numbers

%r: output by original format

Two: arithmetic

A = #0 0 1 1 1 1 0 0
b = #0 0 0 0 1 1 0 1

1: with arithmetic, The binary value of two digits must be all 1, then the result is 1

A & b = 0 0 0 0 1 1 0 0 = 12

2: or arithmetic, a binary value of two digits, as long as one is 1, the result is 1

a/b = 0 0 1 1 1 1 0 1 = 49

3: xor, two digit binary value, the upper and lower contrast is different is 1

# a ^ b = 0 0 1 1 0 0 0 1 = 49

Three: for Loop

The main purpose of the loop is to reduce duplication of code

As example one: Loop code 4 times

1 ' abc123 ' 2  3  for  in range (4):  4      print(" loop:", I)　　　　　　　　

Results:

　　　　　　　　

Example Two: Loop 10 times, show only after 6 times

1  for  in range:2     if i<5:3         continue # without going down, go straight to the next loop. 4     Print ("loop:", I)

Results:

　　　　　　

Four: while loop

1: the cycle of death, will always cycle

1 count = 023 while True:4     print(" Here we go . " , Count) 5     Count +=1

2:while Limit number of cycles, guess Age:

Age = 18count = 0while Count < 3:    input_age = int (input ("enter your Age:"))    if  input_age = = age:        print ("guess Right ! ")        Break    elif Input_age < age:        print ("guess Small")    else:        print ("guess Big!")    Count + = 1  # Each loop counter +1else:    print ("wrong 3 times, Exit.")

　　

5:3-dollar operation

is to display the criteria for multiple lines of printing as one line:

Example One:

A = 1b = 2if a > b:    c = a+belse:    c = a-d  

can be reduced to one line as follows

c = a+b if a>b else a-b

The Format is:

　　　　result  = 值 1 if 条件  else 值 2

If the condition is true: result = value 1
If the condition is false: result = value 2

Six: string Other usages

print (name.capitalize ()), First Capital print (name.casefold ()), full variable lowercase print ( Name.center (10, '-')), make up 10 characters not enough according to "-" to indicate, if not write the default is separated by a space, the string is Centered. Print (name.encodswith ()), prints true or false print (name.expandtabs)), enlarges the String's space print (name.find ("lib")), searches for values, finds early reply values, cannot find a reply -1print (name.format ()), similar to%s (according to photo) print (name.isdigit ()), to determine whether it is a number ============================print ("ad". isalpha ()) , which contains only letters, replies to True print ("a2d". Isalnum ()), which contains only a combination of letters and arrays, and replies to true print ("2". isdecimal), where a decimal number returns Trueage = "" "print (age.isdecimal ( ) Print ("2". isdigit ()), containing only the integer positive print ("al_ex". isdentifier ()) # is not a valid variable name print ("al_ex". isupper ()) print ("2". islower () Print ("2". isumeric ()) print (float ("3.1"), Judging whether it is a floating-point number, not the error print ("3.1". Isspase ()), Determines whether it is a space print (",". join ("alex")), Results: a,l,e,x//* decided to split print ("alex". Ljust (50, '-')), starting from the left to display strings, insufficient "-", print ("alex". Rjust (50, '-')), starting from the right to display strings, insufficient "-" , =================== print ("alex". translate (trantab)), print ("alex". partition ("1")), print ("alex". replace ("ex", " 123 ")), result: al123//* replacement character 

　　

Seven: tuples

Tuples are actually similar to the list, but also to save a group of numbers, it is not once created, it can not be modified, so it is called a read-only list

Syntax: names  =("alex","jack","eric")

Eight: Dictionary

1: the role of the dictionary, why should have a dictionary: because the list query value, need to know the index value, or to know all the values in the sub-list, query is very inconvenient, so the value and query is very inconvenient, so there is a dictionary to compensate for the lack of the list

2: Dictionary syntax, and Features:

Variable = {key,value} # Dictionary

Variable = [value 1, value 2, value 3] # list

Variable = (value 1, value 2, value 3) # tuple

1: in the dictionary key, the key value must be unique, otherwise in the query value, there will be an error,

2: the key value in the dictionary is unordered, the value corresponding to the key is constant, unless it is artificially modified

3: Dictionary Additions and Deletions:

names = {    "stu1101": {"name": "Alex", "age": "$", "hobbie": "girl"},    "stu1102": "Jack",    "stu1103": "rain"}

　　

1): Check

Print (names["stu1101" ["hobbie"])

Print (names.get ("stu1104", "abc123")) #查询stu1104值是否存在, exists to return the value that he looks for, does not exist to return abc123 is self-defined, and does not define to return None.

(1): query all key values in the dictionary

Print (names.keys ())

(2): query all value values in the dictionary

Print (names. values ())

2): Increase

names["stu1104"] = ["zsy", "ABC123"]

3): Change

names["stu1104"]= ' New_value_1 ' #如果要替换值, after replacement, he will replace the key corresponding value of the value of all, can not modify key corresponding to one of the values in the value

4): Delete

(1): Print (names.pop ("stu1101", "abc123"))

# Delete the value of stu1101, if the value exists to return his deleted value value, does not exist on the return abc123,abc123 is self-defined, if not defined, the value to be deleted does not exist, will be an error, so you must add the value of Echo

(2): # del names["stu1103"]

4: Other operations of the dictionary

1): Fromkeys (variable, Value) # change list to Dictionary

Comments

1:dict is a data type, only dict can be used to invoke Fromkeys ()

2: the value for Jack and Eric corresponds to a memory id, so you can tell that the value is one of the values that they point to, so if one is modified, the other will change, 8-4-1. therefore, If you do not want this to happen, you can modify the value values by 8-4-2:

Figure 8-4-1

Figure 8-4-2

2): Items (): Print the dictionary as a list

Use is generally used to cycle the printing of dictionary information: but the efficiency is not high

3): SetDefault (n,m): Find n, if n exists, returns the value of n, figure 8-4-3

If n does not exist, add n,m. (n is key,m as Value) figure 8-4-4

Figure 8-4-3

Figure 8-4-4

4): Update (): Merge two lists, If two lists have the same value, use the newly added value

5): copy (): copies a dictionary: takes up a separate memory space:

(1): Light Copy

* note:1: Copy is a separate memory address, so the two outermost dictionary memory ID is different

2 : The second level of the dictionary ID is the same meaning because, stu1101 corresponding value is not directly in the entire dictionary, he is stu1101 point to a memory id, two dictionary two-level dictionary, and point to an id, so it appears above the situation

Example 1: you can use the copy of this commonality, to achieve the two accounts at the same time the use of a library, as if the bank card of the Child Mother bank card

(2): deep copy, full copy Lianzi dictionary redefined

Example Two:

　　　　　　

Python Learning Path day2