Intro to Python. Python is an interpreted language Can be used interactively Identifiers are...
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Transcript of Intro to Python. Python is an interpreted language Can be used interactively Identifiers are...
Intro to Python
• Python is an interpreted language • Can be used interactively• Identifiers are case-sensitive • Operators: + - * / ** • Arbitrarily large integer
Python Reserved Words
and assertbreakclasscontinuedefdel
elifelseexceptexecfinallyforfrom
globalifimportinislambdanot
orpassprintraisereturntrywhile
yield
Output Statements
• print ()• print (<expr>)• print (<expr>, <expr>, ..., <expr> )
print (3+4)print (3, 4, 3 + 4) print ()print (“The answer is”, 3+4)
Assignment Statements
<var> = <expr> <var> = input(<prompt>) <var> = raw_input(<prompt>) <var>, <var>, ... <var> = <expr>, <expr>, ..., <expr>
x = 5y = 3.9 * x * (1 - x)age = input(“Your age?”)name = raw_input(“Your name?”) x, y = y, x
Decisions
if <condition>: <body>
elif <condition>: <body>
else: <body>
< <= == >= > !=
if x > 5: print “greater than five”
elif x < 5: print “less than five”
else: print “five”
Definite Loops
for <var> in <list>: <body>
Sequences/Lists
• [0, 1, 2, 3] • [1, 3, 5, 7, 9] • range(10) • range(<expr>)
for i in [0, 1, 2, 3]: print i
for i in range(11): print i
Indefinite Loops
while <condition>: <body>
i=0while i <= 10:
print i i = i + 1
Strings
greet = “Hello Bob” str2 = ‘spam’ print greet, str2 greet[0] greet[-1] greet[-3] greet[5:9] greet[:5] greet[5:]
More with Strings
greet = “Hello Bob” str2 = ‘spam’ greet + str2 3 * str2 (3 * str2) + (greet * 2) len(greet) for ch in greet:
print ch,
String and List Operations
• + Concatenation• * Repetition• <string>[] Indexing• <string>[:] Slicing• len(<string>) Length• for <var> in <string> Iteration
[1, 2] + [3, 4] [1, 2] * 3 grades = [‘A’,’B’,’C’,’D’,’F’] grades[0] grades[2:4] len(grades)
More with Lists
• <list>.append(x) • <list>.sort()• <list>.reverse() • <list>.index(x) • <list>.insert(i, x) • <list>.count(x) • <list>.remove(x) • <list>.pop(i)
Other String Operations
import string string.capitalize(<string>) string.capwords(<string>) string.lower(<string>) string.upper(<string>) string.replace(<string>, <string>, <string>) string.center(<string>, <int>) string.count(<string>, <string>) string.find(<string>, <string>) string.join(<list>) string.split(<string>)
Math Library
piesin(x) cos(x) tan(x) asin(x) acos(x) atan(x)
log(x) log10(x) exp(x) ceil(x) floor(x)
Functions
def <function>(<params>): <body>
def main(): celsius = input("What is the Celsius temperature? ") fahrenheit = (9.0 / 5.0) * celsius + 32 print "The temperature is ", fahrenheit, " degrees
Fahrenheit."
main()
def happy(): print “Happy birthday to you!”
def sing(person): happy() happy() print “Happy birthday, dear”, person + “.” happy()
def main(): sing(“Fred”) print sing(“Lucy”)print sing(“Elmer”)
main()
import math def main():
print “This program finds the real solutions to a quadratic” print
a, b, c = input(“Please enter the coefficients (a, b, c): “) discRoot = math.sqrt(b * b - 4 * a * c) root1 = (-b + discRoot) / (2 * a) root2 = (-b - discRoot) / (2 * a) printprint “The solutions are:”, root1, root2
main()
def main(): # months is used as a lookup table months = “JanFebMarAprMayJunJulAugSepOctNovDec” n = input(“Enter a month number (1-12): “) # compute starting position of month n in months
pos = (n-1) * 3 # grab the appropriate slice from the month monthAbbrev = months[pos:pos+3] # print the result print “The month abbreviation is”, monthAbbrev + “.”
main()
def main(): # months is a list used as a lookup table months = [“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”,
“Jul”, “Aug”, “Sep”, “Oct”, “Nov”, “Dec”] n = input(“Enter a month number (1-12): “) # print the resultprint “The month abbreviation is”, month[n-1] + “.”
main()
File Basics
<filevar> = open(<name>, <mode>) <filevar>.read() <filevar>.readline() <filevar>.readlines() <filevar>.write(<string>)
import string def main():
fname = raw_input(“Enter a filename: “)infile = open(fname, ‘r’) data = infile.read() DATA = string.upper(data); outfile = open(fname + “_CAP”, ‘w’) outfile.write(DATA)
main()
Dictionaries
<dictionary>[<key>]
passwd = {} for line in open(‘passwords’, ‘r’):
user, pass = string.split(line) passwd[user] = pass
Dictionaries
<dict>.has_key(<key>) <key> in <dict> <dict>.keys() <dict>.values() <dict>.items()<dict>.get(<key>, <default>) del <dict>[<key>] <dict>.clear()
