Practice, Python

Python. Examples of solving tasks with character strings. Part 2

Examples of solving tasks with character strings. Part 2

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1. Function ChangeCharToStr(). Replacing a character in a string

 

# Replacing a character in a string.
# Parameters:
# - s - source string;
# - c_old - character to be replaced;
# - c_new - the character that replaces the c_old character.
# The function returns a new (modified) string.
def ChangeCharToStr(s, c_old, c_new):
    # Initial assignments
    s2 = ""
    i = 0

    # Symbol replacement cycle
    while i<len(s):
        if s[i]==c_old:
            s2 = s2+c_new
        else:
            s2 = s2+s[i]
            i = i+1

    return s2

# Demonstration of using the method
s = "asd sdks slkdj sss"
s2 = ChangeCharToStr(s, 's', 'X')
print("s =   ", s)
print("s2 = ", s2)

Program result

s =   asd sdks slkdj sss
s2 = aXd XdkX Xlkdj XXX

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2. Function ChangeCharToStrPair(). Replacing a character with another character in a string at paired positions

The ChangeCharToStrPair() function has a code similar to the previous ChangeCharToStr() function. To determine if a position is even, the condition is used

i%2 == 0

where i – position number.

# Replacing a character with another character in a paired position.
# Positions 0, 2, 4, ... are considered paired positions.
# Parameters:
# - s - source string;
# - c_old - character to be replaced;
# - c_new - the character that replaces the c_old character.
# The function returns a new (modified) string.
def ChangeCharToStrPair(s, c_old, c_new):
    # Initial assignments
    s2 = ""
    i = 0

    # The cycle of replacing characters in paired positions
    while i<len(s):
        if (s[i]==c_old)and(i%2==0):
            s2 = s2+c_new
        else:
            s2 = s2+s[i]
        i = i+1

    return s2

# Demonstration of using the method
s = "sad sdks slkdj sss"
s2 = ChangeCharToStrPair(s, 's', 'X')
print("s = ", s)
print("s2 = ", s2)

Program result

s =   sad sdks slkdj sss
s2 = Xad Xdks slkdj sXs

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3. Function DelCharAtPos(). Removing a letter from a word given by position number

To remove a letter from a word at a given position, a slice is used.

# Removing a letter from a word specified by position number
# Parameters:
# - s - строка, из которой удаляется символ;
# - pos - позиция символа в удаляемой строке.
def DelCharAtPos(s, pos):
    # 1. Checking if the data is correct
    if (pos<0) or (pos>=len(s)):
        return s

    # 2. Removing a character through a slice
    return s[:pos]+s[pos+1:]

s = "0123456789"
s2 = DelCharAtPos(s, 0)
print("s =   ", s)
print("s2 = ", s2)

The result of the program

s =   0123456789
s2 = 123456789

  ⇑

4. Function DelChar(). Remove all occurrences of a given character from a string

The DelChar() function creates a new string s2 from the original string s, which does not contain the specified character c.

# Remove all occurrences of a given character from a string
# Parameters:
# - s - the string to remove the character from;
# - c - a character to be deleted.
def DelChar(s, c):
    # newly created string
    s2 = ""

    for sym in s:
        if sym!=c: # all symbols except sym are appended to string s2
            s2 += sym
    return s2

s = "012345363738494"
s2 = DelChar(s, '3')
print("s =   ", s)
print("s2 = ", s2)

Program result

s =   012345363738494
s2 = 01245678494

  ⇑

5. Function DelSubstring(). Remove all occurrences of a specified substring in a string

A modification of the previous DelChar() function is the DelSubstring() function, which removes all occurrences of a substring from a given string.

# Remove all occurrences of a given substring from a string
# Parameters:
# - s - the string from which the substring is removed;
# - sub - the substring to be removed.
def DelSubstring(s, sub):
    # newly created string
    s2 = ""
    index_s = 0

    while index_s<len(s):
        # get substring using slice
        sub2 = s[index_s : index_s+len(sub)]

        # checking for equality of the original substring sub with the current sub2
        if sub2==sub:
            index_s = index_s + len(sub)
        else:
            s2 = s2+s[index_s]
            index_s = index_s+1

    return s2

s = "12344334343455"
s2 = DelSubstring(s, '3')
print("s =   ", s)
print("s2 = ", s2)

Program result

s =   12344334343455
s2 = 124444455

  ⇑

6. Function FormArrayWords(). Forming an array of the frequency of occurrences of words in a string

The FormArrayWords() function determines the frequency of repeating words in a given string. The function returns a dictionary containing string: count pairs. The separator characters are specified as a parameter of the function in the form of a list.

# The dictionary determines the number of occurrences of a word in a string.
# Parameters:
# - s - the string in question;
# - chars - an array of word separators.
def FormArrayWords(s, chars):
    # 1. Take into account that delimiter characters can be at the beginning of a line
    index_s = 0
    while (index_s<len(s))and(s[index_s] in chars):
        index_s = index_s+1

    # 2. Initial settings
    prev_index = index_s # word start position
    A = [] # the list of words

    # 3. Loop for highlighting words in a line as a list
    while index_s < len(s):
        if s[index_s] in chars: # if s[index_s] - delimiter character
            sub = s[prev_index:index_s] # get substring
            A = A+[sub] # add substring to array

            # rewind if multiple separator characters are in a string
            while (index_s<len(s))and(s[index_s] in chars):
                index_s = index_s+1
            prev_index = index_s

        else: # if there is no separator character
            index_s = index_s+1

            # checking if the last word
            if index_s==len(s):
                sub = s[prev_index:index_s]
                A = A + [sub]

    # 4. Formation of a dictionary based on list A
    D = {}
    for word in A:
        if word not in D:
            D[word] = 1
        else:
            D[word] = D[word]+1

    return D

# Demonstration of using the method
# 1. Исходная строка
s = " ,, abc defg hjk, , mm nn, op op mm abc, "

# 2. Array of delimiting characters
chars = [ ' ', ',']

# 3. Formation of the frequency dictionary
D = FormArrayWords(s, chars)
print("D = ", D)

Program result

D = {'abc': 2, 'defg': 1, 'hjk': 1, 'mm': 2, 'nn': 1, 'op': 2}

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Related topics

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